Bill,
The idea is not so much to enlarge the hole as to remove the area of the thread, where it "runs out" and the screw would finish to a razor's edge. This little edge almost always breaks off, so you can see it it you look closely. Try one on a piece of scrap, and you will see what I mean. It might work with a #30 drill, I just use the clearance drill to be sure.
Mike