Just how good is auto-canceling?

[KirinKQP]

How much of an effect does auto canceling Bair or Nair have on my gameplay? Is it an option that I should use when I can? And if so, are there any follows ups that can come off of an auto canceled move, such as into a rest setup or something? When I play against my friends, I land a hit and know I have an ample amount of time to follow up because of the very short lag time, but my poor spacing says otherwise. How could I work on that; should I get better at controlling my aerial drift when using those moves, perhaps become more comfortable with rest combos?

 

[krazyzyko]

Auto cancel nair rest is a thing on floaties with bad DI. Otherwise AC is just good to avoid landing lag punishes.