Ooh! Ooh! Me! Me! I watch some let's players!
Mind you, there are certain, specific ones that I tend to watch more than others, but I do watch them nonetheless.
They can sometimes be pretty good at telling whether or not a game is something you will like, actually, though they probably shouldn't be your only source of info on that if you can get any other info elsewhere, and they probably shouldn't be your source of info on games that are rather story-heavy if you care about spoilers (and, in the event the game is basically ALL story, spoiling the point of the game itself). And that's just reason #1 for watching them!
Reason #2 is that they can sometimes be fun/funny to watch. Reason #3 is that they can sometimes pull off impressive stunts that are really fun to watch. There are, of course, a zillion other reasons I could mention, but I'd rather not make this post any longer than it already is. XD