I've been known to sit out of clan matches simply because of the pressure to win. I definitely couldn't deal with a clan that's entirely based in how good a player you are it seems less fun to me that way. When you do decide to join a clan, be prepared for it to take up a couple of nights a week, if your clan is involved in competitions, matches and scrims. Some people have found it hard to fight burn-out from playing the same game for months on end, and being in a clan has the potential to demand a lot of time and attention from a member. Not that you can't take breaks away from the game - that's to be expected, otherwise you might just burn out and hate the game forever after.
Nobody wants that to happen.
Clans inherently improve your teamwork and make a game a lot more fun to play. They can provide you with people to play against and with, people you can learn from, and people you can teach. It's a great way to meet people and make some wonderful friends. Some clans even hold LAN parties and meet each other in person, which can be great fun. There are all sorts of benefits that can be enjoyed from being a member of a gaming clan once everyone has learned how to deal with some of the negative aspects of them.