So you sand down a somewhat rust-eaten frame, and it's got some pits of varying sizes. You send it to the powder coater, they sandblast it and coat it. It comes home. The new condition of the frame is:
A) All the pits are filled in and the surface of the frame is smooth and beautiful, via the magic of powder coat, which seeks its own level, like water.
B) The smaller pits fill in completely, but the bigger ones now appear as little dimples in the finish. It's not as good a finish as you could get with epoxy and paint. But the bike looks better than it did before, and at least it doesn't keep rusting.
C) Your bike looks like the surface of the moon, only less dusty, and one uniform color. It looks awful, but at least it doesn't keep rusting.