It's micro scratches of varying depth in the clear. If there's enough of them all layered up on one another, they obscure the way light transmits through the clear to the paint. You see what looks like a dull, flat none glossy surface that can almost have a very slighly transparent white look. Detailing is mostly clear coat correction, it's just called paint correction as the clear is over the top and part of it.
Problem is, once you understand it and see it, you can't unsee it
Just re cost, you can make it cheaper for yourself with very little negative effect by requesting single stage machine correction. Slightly deeper scratches in the clear won't be removed, but these aren't the ones that make your paint look flat, dull etc. They will likely still be softened slightly and less visible. If it's a daily car, I wouldn't bother and I'd rather the extra clear coat.