Dropped my All clad copper core fry pan and.....
there is a small dent in the bottom...very small...will that affect the performance of the pan..and how so?
If it didn't crack, the perfomance should be unaffected. Unless the dent causes the pan to wobble when placed on the burner or countertop, which can be annoying. Or if the dent pokes through to the interior of the pan and creates a little nook where stirring implements can't reach, thereby increasing the possiblity that food might burn in that spot.
But you're probably fine.
On second thought, your pan is probably ruined. Better send it to me.
I think that All Clad pots are guaranteed for life. I would e-mail All Clad see what should be done, including getting a replacement.