AC+ will repair/replace under warranty for defects or malfunctioning components.
AC+ includes three instances of ADH (Accidental Damage and Handling) at $79/$99 per incident.
AC+ does not cover cosmetic issues that do not affect the proper functioning of the phone. I.e., scratches, scuffs, dents.
To actually use an ADH the phone will have to have actual damage. A cracked screen, a bad battery, etc.
AC+ is not intended to allow people to walk in on the last day and swap out a perfectly functioning but cosmetically imperfect phone for a new phone. Unless there is a defect or damage Apple will turn you away.
That said, lots of people purposely damage their phone shortly before AC+ runs out so they can get a new one and sell it for higher value.
Whether you think that's okay or not is the real question.