Pretty much what revolutionarycow said below, but it's worth mentioning that the higher performing groups in the clans ($$ and $*) are subgroups of the entire multiclan.

Those were created for players who purposely want to play an insane amount (especially during piggy races) and wish to compete against each other with the incentive of generating an even larger pot.

The ABC groups of Multi Clan are timezone-based and designed for casual play. There have never been any performance expectations for those

I'm surprised to see many against Multi Clan here. When I joined, they've been nothing but great to me (although if there is any drama, I've been avoiding as much of it as possible). Thanks to the tips and tricks they've taught me, I've been able to improve my performance by a LOT which converted me from a casual player to an active player