Burst is mined by hdd, it works with precalculated hashes, stored on hdd. It's NOT pay rewards for sharing space.
It is useful, to store hashes, because you only calculate them once ... not 24/7.
That is true. Whereas Bitcoin and other PoW coins waste a hefty amount of energy, Burst gives a better advantage by being energy efficient. It also opens ways for an average Joe to get started mining in minutes with just a HDD without the need to buy expensive ASIC mining equipment. But still, it would be great for Burst to have data cloud feature. Since Burst is based on NXT, I think that this could be implemented (since the latest version of NXT already has this) Check it out here: https://nxt.org/what-is-nxt/data-cloud/