Proof of Brain is the mechanism by which we use Community Tokens to reward users for their human meaningful efforts. The token is mostly staked, and worth a lot more than people think. But every user should be demonstrating proof of brain in general on Hive, and POB is that concept itself, as a token. Therefore, POB can be used to reward the absolute best content. Do not vote for any SPAM or low value content with your POB stake. You can check out this post on the front end, @darrenclaxton/my-proof-of-brain-introduction