I would say that it is one of the ways to ensure a level of stability of prices and making sure that prices technically never fall down to 'zero' level.
Personally I do not support coin burn for a Proof of Stake Blockchain. We should focus on people trying to maintain their stakes in the system and increase them gradually. What we need to do is to provide people incentive to hold more Steem.
Although burning Steem or sending it to the null account might sound like doing exactly that, but it is a short term and a stop-gap arrangement. We need to create a system where people believe in holding a stake in and not a system where people might want to raise prices by burning coins
Well, the benefits for holding a stake here are pretty good, the profitability for starters, which would increase with price increases.