Some ability and ability unlocks.
So, this game doesn't have a tree so much as it has a bunch of lines. The clan you pick gets its abilities in a straight line for cheap, but you can go to the left and the right to get abilities from the other clans for a way more expensive price (Gets more expensive the more removed from your clan it is)

This means that even if you don't select either of the two DLC clans, you are still missing out on ability selections if you're playing the default version.