The plus is that it slows or even prevents the return of oxidation. Put another way, rust is less likely to become a problem.

The negative, as mentioned by others, is adhesion. Smooth surfaces do not lend them selves well to paint sticking. But it does stick and careful use will leave it stuck for a long time. If adhesion does fail on the chrome plated surface, big deal. Just remove it and removing paint that does not adhere is easy. I have done it many times on bikes that came with the clear coating in place right from the factory. And you know what? The chrome underneath is darn near perfect.

So, for me, I want to protect the chrome plated surfaces. I would never sand unless pitting had actually occurred. These fenders, for example, are a sand and paint over situation. Only rechroming would solve the problem so, I painted over them with Rustoleum, a product that is recommended for use without primer...