It is interesting to me that the brain seems to do useful thought when I let it run free. I've had the experience of going to bed thinking about a math problem, and waking up with the answer, but the answer was arrived at subconsciously. And when I have a difficult problem to think about, I often put my head down, and it seems to other people that I'm sleeping, but I'm pretty sure I'm thinking, even though I'm not consciously thinking, because I will come up with reasonable solutions after this process.
So why do I go through the subjective conscious "effort" of working on problems if my subconscious mind could solve them? I've thought that maybe it has to do with "symbolic processing", e.g., reasoning about things using logic and symbol manipulation. Of course, my brain can do math subconsciously, so that seems like a whole in this theory, but I feel like before my brain can do math subconsciously, I need to build a mental model of the problem. Once a mental model is in place, I feel like my subconscious can "intuit" a solution.. so maybe the conscious mind is necessary to build mental models, and reason about things that are not "intuitive".
Another candidate for what the conscious mind does is adjusting the mental zoom level, and directing what to zoom in on.
In any case, I've tried trying to not control myself, and just letting my subconscious make decisions, and it seems to work. That is, my body does do stuff, all on it's own. It can even talk to people, all on some sort of "auto-pilot".
So.. I'm not sure. Note that the issue of "what does the conscious mind do?" is separate from the question of "free will". Even though I don't believe in free will, I still admit to having the subjective experience of "making decisions". I'm just curious why some of the decisions made by my brain are interpreted subjectively as having been made consciously, and some of them are not interpreted that way.