If you hit with an air counter hit, the opponent is put in a comboable state, for example: if you hit an enemy with an air normal (counter hit), you can land, do a normal than rejump to finish with an air combo. If not counter hit, the opponent won't get hit by the ground normal.
I'm not sure about this, but I remember that you can link something after an overhead counter hit (for example lucifer 6b(?))