I actually find it kind of interesting that acoustic piano players are generally accustomed to sitting on a bench and don't usually vary from that beyond whether or not it's padded or has adjustable height. I know I didn't. Probably 40 years of playing and never really even thought much about anything other than a bench.
However, among the keyboard playing community (where I now hang out almost exclusively), a chair of some kind, usually an office chair, is a lot more common. Maybe it has more to do with setups where people need to move from one keyboard to another, or to a mixer or some other piece of equipment, quickly and easily, either on stage or perhaps in a studio setting.
I do have to admit, though, that having used the latter for so many years now, going back to a bench would not be my preference.