I like OOC rooms.
I spent years on games without them and I often felt isolated. Like I was playing inside a vacuum with just a couple other people. Mostly because the public channel would be too much spam and/or I'd forget to turn it back on after turning it off to rp. So I'd have group or area channels which.....adds to that isolated feel.
Many games, also, don't offer private rooms for everyone. So you find yourself constantly waving off rp if you're just on to do mail or talk to people.
All the complaints about them exist in other means (and can/should be policed by staff). But I absolutely find benefit in them for helping me feel more ingratiated to the game....and I say this as someone who had to have words (as staff) with someone who was causing issues in the ooc room. I'd rather do that and leave people a place to interact than have none and find people not even bothering to login because they feel they're being forced IC at all times.