10-16 confusion

On 10-16, I dimple the pilot hole, then do some drilling, then I dimple all the rest of the holes. Why was the pilot hole its own step?

Also, when it says fill the pilot hole with a rivet, I just put one in and tape over it, or am I crushing a rivet on a single skin? (Sorry for the beginner questions).

The Pilot hole is not used on the tri gear version and enlarged on the tail dragger version. So to clean it up you dimple and squeeze a rivet in the hole assuming you have a tri gear. You can dimple all the holes at the same time I believe. I did