The Only Purpouse being in a Clan are Weekly Rewards!
The most clans started with a couple of friends that know each other for a long time and are always playing together. So when you join that clan, you still have nobody to play with.
I have been in a couple of big clans and always the same story: a couple of core players and everybody only wants to play with them. When i search for a clanmate to play with, they just ignore me.
I play a lot and for me the main reason for joining a clan is that i will have somebody to play Trials, Raid or Nightfall with. In every clan untill now i still had to depend on LFG websites.......while i'm i a clan.
I will not even talk about Trials. No chance to find somebody from the clan to play with. I don't even care about k/d, i just want to play Trials because i like competitive. If you have k/d 0.5 i will play with you. But even then nobody wants to play.
Yesterday i've joined a new clan. Hopefully this one will be better.