We've had slides in both our TT and our current Class C. The benefits of them is more room when extended. They do make a difference. The thing is to make sure that you can access everything when the slides are closed. We could not with the TT, but we can with the Class C.
My opinion is to avoid them if you can. Our next unit will probably be a Class B or maybe back to a small TT (wife isn't on board with that yet). But we will probably avoid slides. Probably won't have too much of a choice on the Class B (the ones we like don't have them).
If you are living fulltime and sit in a place for a month or more, then you will probably want slides.