Pretty self explanatory. An option for a member to report another member if needed. In case this member is causing mass spam or there username is inappropriate or something like that. I found it to be a super helpful feature on IPB, but I haven't seen an add on or anything for this on xF.
I'm inclined to agree, as we've had zero post members sign up only to spam their own profile page via the homepage link and sig. We've put other measures in place to stop this, but I can see why it would be useful.
I'm surprised such a core feature wasn't implemented from the start. Being able to report member profiles would be astronomically more efficient. For forums with large memberbases and a strict set of rules, there will be a large number of members who violate the rules. At the moment, the only way to inform a moderator of members who may be violating profile rules, such as explicit avatars or profanity within their signature, is to report one of their posts. This is not a productive method at all.