You can follow the link the post to read some more details but at present the main thing is simply to burn the rewards (which leaves the system in the same position as if the rewards were never paid out at all), on the theory that many reward payouts are not worth the negative effect they may have on the price as people cash them out. Of course, not everyone will believe that to be the case, and views may change over time. As those views evolve, the amount paid here, and therefore burned, is set by voting.
The main posts are set 100% beneficiary to @null so the rewards are immediately burned by the system. For the comments, the rewards are burned by a bot as soon as they are paid out. Any SP rewards are steadily powered down and also burned by the bot.
In situations when SBD is overvalued (which has happened in the past, but not currently), the process is a bit different and uses the paid-out SBD to maximize the benefit to Steem stakeholders using a buy-and-burn procedure which increases the amount burned and helps reduce the price of SBD back toward its $1 target.