I did an experiment with one of my posts, I paid 9SBD and from the votes I got around 7SBD and 40SP. In this case it wasn't directly profitable, but I presume for some people it is. The main idea is to improve the overall health of the Steemit ecosystem by burning SBD. That will maintain the peg and it will allow the system to continue printing. It's all economics and it can get quite complicated, but the bottom line is that this proposal was made in order to incentivize people to burn SBD.