Stock/ish pistons generally come with some offset in the pin in order to load the piston against the cylinder wall=keeps them quite, grandma didn't like noise in her new car, get it so far?
so that is friction/drag which decreases power a tinzy bit.
reversing them unloads them and wahlah! more power, as for wear? not really of any significance.
It's a good thing, trust me.
And...do you see any offset pins in performance pistons like KB/ROSS/WEISCO?, answer is no.
So what are you building, a stock engine or a performance engine?
