...and yet that is still useful enough to be the right answer for some products. For the camp cooler example, it means I don't have to waste precious space on ice packs, nor worry about water as ice melts. If I put in room temperature sodas, they will be cold within 24 hours, which is good enough to be useful. On cold days I can run it in reverse and have a hot drink at break time. And the cooler/heater itself barely adds any weight to the cooler itself.

As a side note, look up the book 'manifold destiny'. It's all about cooking with one's engine bay. An amusing read!