Generally, moderator flags fall into one of the cookie-cutter categories given in the "flag" sheet. And even when community users choose to type a custom message into the "other" box, the flags require no communication back with the user. The action is simply taken (or not taken), and everyone goes about their business.
But what do we do in those (I imagine relatively rare cases) where a community member uses the free-form "other" box to ask a specific question about their post? For example, after having one of their posts deleted by a moderator, the user who originally posted the answer flags it and asks:
Why was this answer deleted?
How are we supposed to deal with those flags? It seems like a perfectly valid question that is deserving of an answer, but there's no obvious way to communicate back with the user and provide them with such an answer. You could leave a comment on the deleted post explaining the rationale, and the person who posted it would still be able to read them even though the post has been deleted, but there's no way to add comments to a deleted post.
I suppose you could send the user an e-mail, but that seems like a pretty heavy-handed solution. Not everyone wants to receive correspondence for this site over e-mail, and e-mail seems best reserved for extended discussion, not simply answering the question of why a post was deleted.
Certainly I agree that we don't want to make such usages of moderator flags common-place. Perhaps it would be best to advise the user in question to take up the discussion on their site meta. But how do we advise the user of this without the ability to contact them?
I've seen this feature request, which attempts to provide a solution to the question that I'm asking. But I'm not necessarily in favor of adding a new feature. I'm merely seeking advice or input on what the expected practice is in the status quo. Surely this situation arises on Stack Overflow—how is it handled?
