I do it every gig. It's pretty much the standard way of doing things when you're playing pubs and clubs isn't it.
Yes, you do rely on the sound guy a lot!
It's better than just going through the backline in the majority of cases though. In anything larger than a very small room, just a backline will sound terrible.
It's better to hear every instrument in every part of the venue, rather than having to go over by the bar to hear the guitar, stand in the corner to hear the keys, etc etc.
Also, a good sound guy will balance out the instruments, so that everybody is living in their own frequency range - otherwise, although you may sound great on stage, you'll just sound like a mush of noise to the audience I'm afraid - especially if you're on a hollow stage!