Again, with the Claybar, pick the dirty finish of your choice, then claybar just a small area, look at the Claybar, and almost always, unless the vehicle is a total Garage Queen, there will be embedded stuff in the paint, along with whatever is left of the sealant, wax, etc..
I would personally, want to remove as much of this stuff as possible before I began the correcting stage of any vehicle I am working on.
The less amount of embedded junk in the paint, the better the correction stage will be, and the cleaner my pads will be.
Sometimes, just using the Claybar will improve the light reflection through the paint so much (because it removed a lot of embedded stuff) that this is all you will need to do! If your paint is the colors that dont show scratches, swirls, etc., than maybe this is all you need to do, and it will look amazing, because the Claybar cleaned a lot of crap out of the paint, and allowed the light to go into it and reflect back out of it straighter.
Will the Claybar and washing get everything off so that your correcting pads will be perfectly clean when you use them? No, they will still get some junk out of the paint that is mixed with the compound product, a little of the paint topcoat, etc..
But the best part is that there is to me, less junk swirling around the paint when its being corrected, to give it the opportunity to scratch the paint further, etc..
I am sure that if the Claybar wasn't needed, it would have never been invented back in the middle 1980's then.
To me, the only paint that would probably not need to be Clay'd would be brand new, just out of the paintbooth, assembly line, etc., paint that has not had an opportunity to be hit with all the crap that falls out of the sky - especially in big urban areas.
I try to keep our 4 vehicles as clean as possible all year long with washing, etc., and the ones that stay outside always need to be clayed, even if they didnt go but a few thousand miles that year. The ones that get the garage still need it to, but not nearly as much as the outside vehicles.
Dan F