Why do people want to join clans anyway? I can understand clans for RPGs where you can actually benefit from your team members, but a FPS? I don't quite see any purpose here, especially when all of your clan can't choose to join one side.
Camaraderie, community, and fun. I'm in the
ATF clan and although we have a competitive team, we also have well over 100 members just in our team fortress 2 division alone that play the game non-competitively.
What it boils down to is we always have good friends to play with, as well as a well policed atmosphere on our public server. We also organize at least 10 or so special events for members only on our private server which can pretty much be anything. We've had Drunk Fun Nights, Map Tests, Class-Based special rule events (random classes, limited classes, all one class), Westside knife fights, mini-tourneys, etc.
Also when a new game comes out, there's tons of people i already have in my friends list for each one. Left4dead, Quake Live, etc. without having to venture onto pub servers with a bunch of phucktard individuals. Not to mention I always have a few fellow "team players" I know I can count on and it keeps the game fun. If we dont get put on the same side, the small "rivalries" that can come up with clan members are good fun as well, cuz' no matter how bad that person is stomping you, you can smile about it, laugh, then post embarrassing photoshopped pics of them in the clan forums.
Even the new release of UT3 and a few of my clan members getting the game for the first time is the sole purpose I bothered to re-install mine and register it on steam.
These are VERY LARGE benefits in my opinion for being in an fps division of our clan.