Re: Restoring a racket
In terms of the material strength, it can be really bad. Every scratch takes pieces of the fibers used in the composite material, thus weakening the material. Every little scratch can weaken your racket, but it will not catastrophically break because of a few scratches anyway.
Theoretically, you can restore composite materials with small patches of fiber-reinforced polymers (the exact same type used in the racket), but it's not an easy job, so it's not used in practice.