Moderators have access to a page which shows recent chat flags from all the rooms on a particular chat server. This is a useful tool, however we cannot see the actual textual content of the flag on a post, we can only see how it was handled, the number of flags on it, and the text of the chat message.
Especially for flags with custom messages, that information is pretty important to preserve if you want to understand why the flag was handled the way it was. And there are certainly times when you want to do that, for example if another mod, from another site say, handled the flag instead of you. Or, if you handled the flag but wanted to review the message some time later.