I think it's so you can have them do things like lock threads if you want them to, as that's how I locked an old RP of mine.
Terraria Community Forums
Ivyss
I meant like your own profile.
Techhunter_Talon
@Dragonwolf73 more or less has it right on why you can self-report.
So they'd have to find a reason to ban you.
Though I do wonder why it's even an option to report yourself.