I am not a guitarist.
The other night, I saw Stacey Earle (Steve Earle’s sister) and her husband Mark Stuart perform. Stacey is a fairly talented songwriter (though not in her brother’s league) and Mark is mediocre songwriter but a talented guitarist. Through the entire set, Stacey was using a capo, while Mark was playing the same songs in the same key and never used one.
Thus the question. Is a capo a crutch for a weak player or is it an essential tool that some parts cannot be played without?
The answer is generally “yes”, with a critical exception: there are some guitar parts which rely heavily on the convenience and tonal qualities of open strings, and capos can allow people to change keys while preserving those qualities. Even a good guitarist sometimes takes advantages of these qualities to produce a great sound.
Most guitarists who use capos aren’t really in it for the guitar playing, anyway. They just want to strum or fingerpick some chords to accompany their singing. Musicians who use the guitar as their voice don’t use capos because it is limiting and they don’t really need it anyway. They know how to play the chords and notes they want to without it and make them sound just as good.
Sometimes but not always, and sometimes but not always.
A less skilled player may well use a capo as a crutch, e.g. using it to play key of G forms when the song is in A, because they haven’t learned the needed chords in the key of A yet. I wouldn’t use the word crutch for someone still learning, though I’d say it could apply to someone who has decided not to learn more.
Even highly skilled players aren’t necessarily equally adept in all keys in some music styles. One may find himself in a situation where he knows a song well in one key, but has to accompany a singer or another instrument that demands a different key. There can be a world of difference between the fingering (for picking) and chords used to play in C vs. those used to play in Eb. I know some knock-your-socks-off players who use a capo for some numbers because it makes a lot more sense than spending the time and energy required to master every key.
It’s not unusual for guitarists to intentionally play different forms on a song together rather than both play everything the same. It adds some tonal richness. One way to achieve that is for one to use a capo while the other doesn’t.
I use one because I am lazy. 
I play guitar mostly because I like something to accompany my singing (which is something I do when I’m bored and by myself) and I can’t be bothered to figure out how to convert chords into a key in my voice range, especially if the key is something like E minor or something.
I can convert between C and G with minimal effort, but everything else, on goes the capo.
Also, there are differences between the nature of chords from one key to another. While any tonic (major) chord uses the same three notes from its scale, the order and repetition of those notes are different between, say, a G chord and an A chord. Someone perfectly capable of playing A forms may choose to use a capo and play G forms because they prefer the sound.
Then you have lazy slackers like HazelNutCoffee. 
I’m one of the cases The Bith Shuffle mentioned. I’m a singer who strums chords for accompaniment. I’m reasonably proficient at doing that in several keys, and often choose to not use a capo at a jam when others are using one, or to use one when they’re not. This is for the tonal variety and often requires sight-transposing. But I see no compelling reason to get proficient at all the chords I would normally use in keys like A flat or E(f*cking) flat. It’s not a matter of laziness, it’s a matter of it not really making sense for my purposes.
OK. In the case of Stacey and Mark, she was playing almost exclusively strummed rhythm parts to his leads, some of which were, oddly, played with the fingers of his left hand over the fretboard, palm facing down.
Tamerlane beat me with 2 of my favourites in Ry Cooder and Richard Thompson and a quick look thru’ my live music videos have the following “quality” guitarists using a capo
Warren Haynes
Rick Parfitt
Rory Gallagher
David Lindley
Lonnie Mack
Dan Crary
John Martyn
Rory Block
. . . so,no, I don’t consider a capo to be a crutch or indicative of a lazy player.
-Mitch
Proud user of a Schubb for over 30 years
I get the whole “you should be able to form the same chords without using a capo” from the anti crowd, but I submit there are some songs, that unless you’ve got a sixth finger at your disposal, there’s no way you could play withOUT using a capo.
Take “Here Comes the Sun” as an example. I play it with the capo way up there on 7 and I must say, it sounds pretty good. Without a capo I know I personally couldn’t duplicate the sound and I would challenge someone to do so without using a capo and simply barring the chords.
Same with “Every Breath You Take” with capo on 2. I can’t see how you’d get the same song without the capo.
All that being said, I will say Capo+Electric guitar = Just wrong
If you want to play a Smiths song the first thing you have to figure out is which fret Johnny Marr put his capo on.
Some of us think this guy was a pretty decent player.
I’ve played over thirty years, and I consider a capo a perfectly legit tool. I’ve never been big on treating music like an athletic competition: the goal is to make music that sounds good.
In the unaccompanied, acoustic style that I (and Delta blues legend Robert Johnson, the guy in the picture) specialize(d) in, no amount of skill will enable you to play a song in, say, the open G position, in G sharp. This is why you see so many accomplished solo players using them. As someone upthread noted, open strings come into play, and this is even more the case when playing solo, where you have to play the bass, chords and melody at the same time.
It definitely sounds less boring if you can play G-position songs in a G#, A, A#, etc. And this isn’t even counting the already-raised point about matching the range of a voice, or other accompanying instrument (I play harmonica too).
And Captain Mumble, I agree that Shubb rules, but without the letter ‘C’. 
A capo is not cheating if you are using it to capture sounds or perform music you could not otherwise play, especially on acoustic instruments where the timbre of open string chords is much different than closed position.
Albert Collins called, and he said he wants to beat you up.
I use one on one song because I’m lazy AND I like the way it sounds. It gives you a sort of distressed tone that is a nice change of pace.
A capo is an approach to playing, as most other posters have said. It is no different than any piece of guitar gear - if used by the right hands, it can enhance a player’s sound. It can also be used as a crutch. And sometimes the line is blurry
I use it to imitate the sound of a lute in classical pieces. It brings all the strings up a couple of notes, which is supposed to (according to my teacher) bring it more in line with a lute.
Depending on the parts, those played with a capo and those played without sound different on a guitar. I’m not a guitarist (although I know the basic chords and songs), but if you’re playing a song with a lot of open chords, it sounds a lot more sonorous capoed than barring all those chords because they’re in a different key. It’s a different tone.
Lemme put it to you this way - you get a gig playing for a country singer. She does her entire rep. in the keys of Eb Major, Ab Major, Db Major, f minor and Bb minor, because that’s where her voice sounds fantastic. Everything calls for big open ‘campfire’ chords. As I see it, you have four options - play with a capo at the first fret all night, tune the guitar up a semitone, come home with the f*ckin’ sorest left hand you’ve ever had or turn down the gig. I, personally, would take one of the first two options. Am I lazy or efficient? I dunno…
Bruce Cockburn has been known to use a capo on his electric - Tokyo is the first number that comes to mind. I remember figuring it out by ear and thinking “Man, how does he do that?” When the book of transcriptions “Rumours of Glory” came out and it said Capo II, there was much head-smacking… Why didn’t I think of that?
In accompanying singers, the singers get to choose the key. Those Schubert and Mendelssohn transcriptions are awkward enough without trying to transpose E Major down to C#/Db Major…
I got into a similar argument with a guy who runs a guitar store in Victoria. His opinion was that you should always play in standard tuning without a capo. After a few minutes, there wasn’t much more to say - I use alternate tunings constantly and capo anytime it looks like it’ll make things easier. I’ll also revoice things to make the transitions easier. Am I lazy or efficient? I dunno; I’m too busy playing…
I don’t care what a guitarist uses to produce his sound, the end result is the only thing that matters.
(The best guitarist I ever saw used a capo, as well as a single-string pickup on the low-e string that added an electric bass accompaniment to his playing. He was with a guy on a bouzouki, which might have influenced his capo use.)
When I use a capo it’s lazy…When David Wilcox uses a capo it’s another tool in his toolbox.
What I’m driving at is that as the rankest of rank amateurs I could not play the same song another way and have it sound good to other people. It’s pretty dodgy with the capo. Accomplished players can use a capo to make a different choice. If they forgot to bring them though, they wouldn’t have to cancel the show.
