Some interpretations say "By masking a secret value with a uniformly random zero sharing, the masked value appears to be a random value drawn from a uniform distribution. This randomness helps protect the privacy of the original secret value, as it becomes indistinguishable from other random values. Using zero sharings to mask secret values helps maintain both privacy and correctness in MPC protocols". But the shares generated in Shamir's Secret Sharing are usually uniformly random, why need mask a zero sharing again? In which case the zero sharing is necessary?