NOC's can be useful but they would rarely help improve your credit file. Companies must read this information but do not have to do anything about it.

The usefulness comes from the fact that after credit scoring your application they see you have bad credit but also that there is a NOC on file. They then read this and can take these reasons into account - from my experience I have seen ones explaining that sudden reduncy or family problems have caused credit problems - and instead of the application being declined the companies would ask for further info or decide to proceed.

HTH