I have an inner voice when I think about dialogue. When I construct a discussion in my mind. And only then.
I don't use an inner voice when I think about other things, how to do things, or figure out problems. Way too slow, and after all you can't use an inner voice to figure out how to get through a tricky four-car driving situation. You have to figure out what do do by entirely non-verbal means.
(Just to add - I also don't use an inner voice when I read, unless I decide to. And when I do, reading slows down to a crawl, obviously. So in general I don't)
It's not solely about the inner voice. Abstract concepts, symbol manipulation, mathematical logic and reasoning are for the most part "linguistic" constructs.
I don't use an inner voice when I think about other things, how to do things, or figure out problems. Way too slow, and after all you can't use an inner voice to figure out how to get through a tricky four-car driving situation. You have to figure out what do do by entirely non-verbal means.