The sleep function is pretty nice, but I like to swap games relatively frequently; so being able to save frequently is still critical for me. Plus at the time, I was just playing on my personal computer, so I couldn’t leave it running, even if I wanted to.
For P5R, I suggest only playing for an hour or a two at a time; I think it helps keep the game from dragging. For me, it helped keep the exploration aspect fun since I didn’t have to rush to the end since I was probably not getting there in this sitting anyways.