The main reason you'd want proofs to be checked by someone else, at least initially, is to get a feel for writing clear, rigorous and tight proofs. Much as a no

The main reason you'd want proofs to be checked by someone else, at least initially, is to get a feel for writing clear, rigorous and tight proofs. Much as a novice programmer should have their code reviewed, a novice mathematician needs to have their math reviewed for common mistakes and pitfalls.