This allows people to avoid uncomfortable situations (like someone going @ic in the middle of a private dance on the back room of a strip club) or to avoid unlawful escapes from metagaming players.
If someone uses @ooc as any other advantage than leaving the game when something comes up and it's not a safe place to log out, they'll regret it.
If you feel like someone has used @ooc to their advantage against you, xhelp. There doesn't need to be an ugly OOC mark in the game showing it.
1) You don't see your nemesis in a bar. You walk in and then they come out from @ooc. You'd never have stayed there if you had known.
2) You are being shadowed but you don't know it. You go @ooc for an hour. The stalker loses his window.
3) You lock yourself in a hotel cube that had an open door. Someone else comes from @ooc while you're repairing a sniper rifle.
Not sure if you guys would get what I mean...
For instance, there was a situation where I really needed to @ooc, but felt that others would think I was escaping or had bad sportsmanship. So I just afk'ed and faced the consequences.
In addition, when you really want to let someone know you are going to afk and be back in a moment, but could not (due to the circumstances such as being in a different room), this is very helpful.