Why Claim Your Subnets?
Because then you will get those fun and cheerful security notices! Yay!
Seriously, ISO monitors all campus IP address space. When we find a problem we notify the Security Contact that claims the subnet so they can fix the problem. If we cannot contact anyone, and the problem is serious, we will block the IP Address. Now you have to troubleshoot a connectivity issue without knowing the underlying reason and you still have a serious security issue.