I am aware that it is probably better not to have too many meta-tags such as homework, soft-question, big-list or reference-request. Despite of this I'd like to ask other MSE users, whether they would consider tag of "check my proof" questions useful.
We have a lot of such questions and they are - to some extent - different from questions asking about some mathematical fact. In these questions the answerers are expected to say whether the proof provided by OP is correct and suggest improvements related to both mathematics and writing style.
I can imagine that some users don't like answering such questions (since reading long proofs of other people might sometime be boring, especially if the proof is written in rather unclear manner); and probably there are some users which enjoy answering them (since the OP has shown some work and this seems to be a very straightforward way how to help them improve proof-writing abilities).
This might also help avoiding premature closures of questions. (I believe that a question asking whether a proof posted by OP is correct should not be closed as a duplicate of another question asking about a proof of the same result. I would be careful about closing questions in the other direction, too.)
On the other hand - as I wrote before - I don't like the idea of increasing the number of meta-tags.
So probably the best thing to do is to ask what is opinion of other users.
EDIT: And in case you think it would be useful, perhaps you could suggest the name of the tags and perhaps also places, where some information about this tag should be added. (If we create such tag, it might be added to the post about meta-tags I linked above and perhaps a comment template could be created...?)