My personal experience is my visual imagination is far more vivid but my verbal reasoning is much diminished. I've semi-consciously thought through and planned social situations, and I hazard that it might be useful in artistic fields or in design, where what is important is to 'experiment' with lots of possible visual designs then pick a single one, which diminishes the problems caused by not taking notes as you only have to remember the final result. (Plausibly the reports of people waking up with fully formed paintings/music are semi-subconscious instances of this.)