Autocancels are nice, but have limited uses, since you have to start the move at the beginning of the jump to pull it off. If you space is fair correctly, most characters have a hard time immediately punishing it without an auto cancel. If you think about it, it doesn't really save you much time: you have to use the attack in the air on the way up, so you just experience the ending lag of the move until you land again, instead of the landing lag. Landing it on a shield isn't really much different either way; I tend to prefer short hop / fast fall fairs instead of going for the auto cancel. Back air is more useful when autocancelled imo, due to how fast that move comes out.
