Quite often, the OP will have come up with a proof of a result and needs to be assured of its correctness. The corresponding question is “Is my proof correct?”. If it is so, then the logically appropriate answer is simply yes.
The reason that no further justification is needed in the answer is that the OP has already provided the justification, in the proof, which she demonstrably understands and believes by virtue of having written it.
Nevertheless, just yes appears meagre. It invites doubt: “Who is this person presuming to arbitrate on the correctness of my proof?”. Unless the answerer can boast a stellar reputation score, some additional remarks to demonstrate the answerer's scrutiny and understanding of the proof would be welcome—for example, comments suggesting some stylistic improvements in the structure of the argument.
If the proof is wrong, then in any case a bald no is quite inadequate: The answerer needs to explain where the crucial mistake lies.