Up-air into fair can continue combos on faster fallers at lower percents.
Down-tilt into up-air or fair is good against a lot of floatier characters.
Dash attack into fair is a thing on faster falling characters.
Up-tilt into fair as well on faster falling characters.
down-air into fair is okay on some platform tech-chases if you read it.
Up-smash into fair is okay on some ground tech-chases against faster fallers if you read it.
If fair doesn't kill, it often leads into an edgeguard, so don't always think about Sheik outright "killing" the opponent.