According to Super Regeneration - Boku No Hero Academia Wikia
This Quirk has the ability to regenerate any sort of injuries on the user's body, such as missing limbs, at incredible speeds.
All For One once stole and tried to use this Quirk to heal himself from the heavy damage All Might caused to him, but because his body had already cicatrized those injuries, the Quirk had no effect and was considered useless.
So, because he couldnt heal the injuries he already cicatrized, he considered this quirk was useless. That doesnt seem to have any sense. Why he didnt keep the quirk to heal new injuries in new battles? That would seem to be a very useful quirk, even if fighting All Might again.