Frank Turley talks about the "Three R's" of tapping. Rest, Rhythm, and Rumination (. The rhythm thing has already been addressed. I have about as much rhythm as a frog in a blender, so tapping anything isn't going to help.
Unless I'm forging something humongous, I don't need to rest (that happens when the iron goes back in the fire for the next heat).
Rumination (thinking) doesn't work for me either since I'm an honor grad of the "what I wish I had done school.
All seriousness aside, I guess there isn't anything "wrong" with tapping, lot's of good smiths do it and if it helps, good.