Like, does the guild get a collective character buff or ...something? Is it just to look pretty?
Claiming keeps and other ressources has advantages:
- Your guild store will be accessible to all alliance members inside the keep (they can't sell things, but they're able to buy off your guild's supply).
- You're able to upgrade/improve the keep or ressource, e.g. making the guards more powerful, adding new guards, etc.
- It's some kind of status symbol as well even if this point doesn't have any direct gameplay impact.
- In DAoC you typically got warnings to guild chat when/if guards of your keep died. I don't think this is in the game yet, but I could imagine them adding stuff like this later as well (unless it's in there already, didn't claim anything so far).