You also get meta-physical recognition of your membership, which includes allies as well. Every group in the Dresdenverse has enemies; but they also have allies, and groups that might not want to tangle with whatever group you are a member of.
Example: an NPC in my game is the Emissary of Summer in the city. Yes, he automatically has the enmity of Winter. But he also now has some measure of respect from all Summer-aligned Fae and changelings, and the respect all of Summer's allies in the region. Smaller groups (like the local ghoul clan) may not like him. But attacking the Emissary also means attracting Summer's attention. Maybe they won't care what happened to their toy...or maybe they'll find it a handy excuse/ casus belli. Why take the chance if you don't have to?
