Look at the proofofbrain.io

At the bottom it says "promote post"

This is really sending funds to Hive account@null (This is one way to "burn" funds)

Your post is then listed in the trending section for a while. The advantage is visibility. Every once and a while someone looks through the trending section and sees your post. If you offer something they want on your post then you are in business. You are free to use "post promote". I try not to overuse it... Maybe start with one post promoted to one POB and see if there is a difference. It's one use case for POB.