It is an incentive to keep around gear that can't normally pay for its electricity. Mining gear that isn't online 24/7 but can come online when the need arises is useful to counter a temporary 51% attack.
Interesting point. So miners would stay online and only mine blocks that they know would be profitable to them?
Presumably there would be a lot of such miners, which would increase competition for those more profitable blocks, which would essentially dampen out the expected value of the rewards. I wonder how the math works out.
