I love playing with animal companions and usually when playing if I want my companion to stay on a baddy while I move elsewhere I command it, but if I'm moving I've always moved the animal with me assuming that my animal wouldn't be there if I wasn't. Up till now the DMs I played with seemed to operate under similar auspices. I have been periodically playing a campaign where every game the question of whether or not my animal companion would follow me, or stay in one place without a command has come up, and I have yet to find a definitive answer. One example was leaving a smoke filled room, another was moving around a pillar for better fighting position, ironically enough leaving my companion there would have left it with an attack, I just played as I normally would with my companion. Another situation was whether or not my companion would attack to defend me if I was down, but that seemed a little less likely
