Prepping includes removing tar, bugs, rail dust, scratches and swirls. I usually start my prep with a decon kit (accomplishes the same thing as clay, with less effort), followed by a strong compound on scratches. I will usually use Menzerna PG and a 4" pad to level major scratches.
I follow with a swirl mark remover (I've tried every new one on the market, and I keep coming back to Optimum) to get rid of swirl marks, small scratches etc. If there is any hazing left, I use Menzerna PO85RD to finish out.
At this point, the prep work is done. The paint has a hopefully flawless finish, and then you can wax/seal/glaze to your hearts content. On a perfectly prepped surface, even dollar store waxes will look pretty good. One cannot say the same for high-end waxes on a poorly prepped surface.