You can use this to equalize temperatures on one chip, using it like a changeable heat-shield, so instead of hotspots, you artifically keep some heat from escaping from colder areas too fast which could prevent stress induced cracking. It's better to keep whole chip at 70*C than a one small area at 70 and other areas at 30. Then when heat load from that one small spot vanishes or is moved to other spot, you can change your heat mask on the fly.