There are two commonly found brands of pedal taps. Park and Hozan.
The Park is a standard plug tap and is great for cutting new threads. I do this on an almost daily basis, see http://bikesmithdesign.com/Short_Cranks/shorten.html But I wouldn't use them for restoring old threads as they remove metal instead of mashing it back into place.
OTOH the Hozan is more of a thread former, lousy for cutting new threads but great for restoring old. They taper gradually along their entire length so the further you screw them in the larger the hole gets. I prefer to start them from the back, going in only far enough to get enough threads to come in from the front. I try to only screw them in as far as necessary to get a tight fit on the pedal threads.
To avoid overtightening, always remember to grasp the pedal wrench in the middle of the handle when installing pedals.