I have been making Margaritas for myself and my family for a little while now. I follow a bar manual as I make it. And not being one to break with tradition, I rub the citrus rind on the rim and salt it just like they say. But strange as it may sound, I still don’t know: what exactly is rubbing and salting the rim of the glass for? What is it supposed to do for this drink? And what is the recipient of the drink supposed to do with the salted rim? I notice people, be they in restaurants or at home, typically just ignore the salted rim anyways. Are they drinking this drink the right way?
Be sure to use margarita salt, however. I’ve had margies at places that used table salt. It tends to fall off the inside rim and collect at the bottom, salting the whole drink. And margarita salt just plain tastes better.
Properly done, you take each sip of the drink from a salted part of the rim, working your way around the glass. If you work it right, the last sip uses the last bit of salt. Then you order another round and start all over!
But, it must be said, that after having gone to the trouble of salting the rim, in my experience most bartenders then drop a straw into the glass, and as the OP points out, most people then sip the drink through the straw, thus destroying the point of the exercise. Strange.
When I was quite young, I was told they put salt on the rim of the glass to help kill germs that may have been left there by the last person to sip from that glass.
I know, I know. It sounds like bullshit, but in the interest of completedness.
Really it goes back to the traditional Mexican ritual for drinking straight tequila accompanied by salt and a wedge of lime (or lemon). You first put some salt on the back of your hand between the thumb and index finger. You then lick the salt, down the shot, and then bite into the lime wedge. This procedure helps kill the taste of cheap tequila. In the same way, in a margarita, you lick the salt first as you take a drink, and then drink the tequila combined with the lime.
