If he's a self-leveler like me, then he has the issue of running out of BPs as the GB levels up. In most of my cities, at some point or another, I end up having to find GBs in my hood to dump FP on because all of mine are at max level for the BPs I have. This is why I chose the Jester's Stage whenever I got a Feast and Fables Selection Kit, despite the fact that it gives defense boosts, so I would have a steady stream of BPs coming in even when I'm donating to my own GBs.
So...if someone is filling that last level he has BPs for, it leaves him without being able to donate to it until he finds the missing BP(s). Of course, he would run into this problem sooner or later anyway, so it's really just a question of timing rather than any real harm.