It would be, in my mind, beneficial to have the option to turn off your champion's voice in response to move or attack commands.
While I recognize the need for immediate audio feedback to a move command, for some characters and according to peoples' personal tastes, it can be extremely grating to hear them talk all the time.
As an amusing anecdote, the one time I played Annie, I was rage swearing at her every time she said something, because her voice was incredibly displeasing to me. I'd be OK, maybe, with Annie, if I didn't have to hear her talk.
This is not a complaint about the voice acting overall, I think it's awesome, or on Annie's voice actor in particular, it is just my personal opinion that being given the option may incline people to play certain characters more often. (Cho'gath or Annie, etc.)