Yeah I'm not talking about the shim crap..... people brake tap for 2 reasons, both listed in this thread.

1. Hub distortion in corners can force the pads away from the rotors creating a soft pedal, so you can pre-tap to get everything snugged up.

2. Just checking to make sure you're brakes are good to go when barreling down the straight at 170+

If someone's brake tapping on a striaght then it's #2, if they're brake tapping in a turn or just after one then it's #1.