A Claybar is a paint cleaner. Its one and only job is to remove bonded contammination on teh surface of teh pain (or Glass, or allow wheels). When properly applied, the claybar itself never touches your paint. It glidesover it on a layer of lubrication (detail spray).
The benefit of using detailing clay versus a traditional car polish or cleaner wax (to clean your car) is that claying is faster and it does not physically wear on the pain finish.
By Comparison, other forms of paint cleaning use chemicals and abrasives that thin your car pain or clearcoat over time which contributes to prematur wear.
One again, a clay bar cannot remove paint imperfections such as switl marks or scratches. it also won't improve the shine. What it will do is remove the gringe so you can see a bright, clear finish before applying a sealer or wax.