I recall in the late 80s/early 90s many households had these VHS rewinders. Since these rewinders served a function that the VCR served as well, for the life of me I cannot figure out why these were so prevalent.
Were they used to extend the life of the VCR?
-R Incognito
Yeah, apparently rewinding it using the VCR’s rewinder would wear out the film much faster and ruin the tape. Or so they said. I’ve never really seen any tests that prove it one way or the other. It could have been a scam, I guess.
It did rewind the tapes much faster than a VCR though.
Plus you could begin watching the next movie in your marathon without waiting for the first to rewind.
It also let you get on with watching another tape. (Daddy! I wanna see Cinderella!) Some decks were s-l-o-w-w-w at rewinding a T120. (Daddy! Where’s Cinderella!?) IIRC, five minutes was not uncommon. (Daddy!!)
Oddly enough, storing tapes “tails out” is somewhat better for longevity - in a played and un-rewound condition, the tape is very smoothly rolled on the spool. The edges are even and the overall tension is uniform. Rewinding usually leaves you with tape edges sticking out of either side of the spool and some lengths of tape may be slightly stretched and some may be more loose. The only downfall to this is that you still need to rewind before watching it again. (Daddy! I wanna watch…!)
That’s why my family had one. Keep the four kids from going off the rails on rainy days…
I thought that they were intended to preserve the mechanism on the VCR machine, not the tapes.
Oh - and as the father of 3 kids, I can tell you their preferred solution was to simply not rewind tapes after viewing, and figure it could be done by the next person wishing to watch it! 
Also, when the tape rental business first got hot, there was a $1 rewind fee if the tapes weren’t rewound when you returned them.
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Rewinding was tough on the motors of the VCRs. A rewinder was cheap (and could be replaced easily if broken), usually faster than the VCR, and let you rewind while another tape was playing or recording.
It wasn’t absolutely necessary, but was a useful convenience.
I agree that the main purpose of the tape rewinder was to prevent wear on the VCR. That’s also why I got one of these for my DVDs.
I had a rewinder or still have in the basement some where that had a nasty habit of yanking the tape off the spool, so I had to be careful to stop it before it came to the very end of the tape. Those VHS tapes were not as easy to open and fix as the old cassettes.
I remember getting a copy of Dances With Wolves as a freebie from McDonalds. It was a long movie on a single cassette, and had the specific warning not to rewind it in a rewinding device because it could damage the thinner tape strip used.
Yeah, most rewinders were horrible… full speed, slamming to a stop only when the tape ran out. A weak tape or tape leader could easily snap, or at minimum pull out of its take up reel… used to hate hearing the sound of a rewinder with a freely spinning motor… meant there was a VHS cassette to fix. (Or Beta-- I have a Beta rewinder sitting around somewhere.)
Marginally improved VHS rewinders were released over the years to include optical sensors that detected clear/translucent tape leader and slowed/stopped the mechanism before yanking the tape apart. Good, except for cassette with no leader, or an opaque leader.
A few also could roughly calculate how close to the start the rewind had gotten by measuring the angular velocity of the take up reel-- the pay out reel would spin backwards at a constant velocity, but as the amount of tape decreased on the take up reel, its velocity increased-- and slow the rewind near the end so the tape wouldn’t snap. Good in theory, but cassettes outside of the T-120/160 length (especially the smaller tapes used for 15/30/60 minute TV specials, or the cheapo LP/SLP bargain tapes) often used larger diameter hubs, which makes such calculations pointless.
Please note some peoples VCR’s ate tapes trying to rewind. Using the rewinder let them use the VCR for a longer time. I noticed the part that caused the failure was always the same little plastic wheel in almost any VCR made. The wheel would start binding and slow down drastically because it was rotating plastic on plastic instead of a proper bearing between.
I think it would help. I had three old VCRs and all of them were about 10 years old before I ditched them and at the end, on all of the VCRs the FF and the REW buttons would not work.
I could hit play and it was fine. Then I could hit PLAY+REW or PLAY+FF and it would work that way, but it seems as if the FF and REW buttons just quit or the mechanism that FF or REW quit
My husband was extremely pleased with the rewinder that I got him for a present, back when we only had a VHS system. He and my daughter would often go to the video rental place on Friday, pick up half a dozen movies, and spend the next day watching them. VHS machines were often slow to rewind the tapes.
I guess, “Please be kind - Rewind!” doesn’t mean much to people who were raised on dvds. 
Sometimes you’d also get - “To Play is Human - To Rewind is Divine!”
When the local rental (other things too, it was a Hastings) place started renting DVDs, they tended to keep sticking the “Be Kind - Rewind” stickers on the DVD cases. It was good for a mild chuckle.
The Magnavox VHS deck I remember from my childhood would auto-rewind if the tape hit the end. Did they all do that?
No. Some would auto-eject at the end of a tape.
Mine did both!
Because of the speed, it was also useful if you realized at 11:50 that you had to get the tape back to the rental place in 10 minutes and it was a seven minute drive.
–Cliffy