Like most have said, the majority of swirls come from improper washing & drying technique.

Not quite - there are particles that sit on the paint surface that do not come off with normal washing. When a wax is applied either by hand or machine these particles get plucked off but remain on the pad and scratch the surface. A quality clay bar system will remove these particles and absorb them into the clay away from your paint surface without causing harm. Than a wax can be applied safely since your paint surface is now baby butt smooth.

I use the Griots garage system for flaw less results! Others work as well.