In order to remove a scratch or any other kind of below surface defect you must remove a little paint.
In order to remove paint best, the pad on a DA Polisher needs to be rotating, not merely vibrating against the paint.
To keep the pad on a DA Polisher rotating you need to keep it flat against the paint and you can't push to hard.
If you buff on a curved in the body panel, or on a body line, as soon as you have more pressure to a small area of the face of the buffing pad this pressure will cause the buffing pad to stop rotating, thus stop removing paint.
Taking all of the above into consideration, plus the fact that you can exert more pressure with your fingers pushing down on a wax applicator pad hand you can with a 6" or 7" foam buffing pad, for some defects, the right way to remove them is by hand or a rotary buffer, not a DA Polisher. If you don't own a rotary buffer and/or don't know how to use one then you always have the "Hand" to fall back on and that's one of the reasons we always teach both hand techniques and machine techniques at all our classes.
Make sense?