Well, for that matter, a giant "heatsink" like a desk, where a lot of realtively heat-conductive material is in contact with the bottom of the laptop, is better than a lap!
Your desk will get warm, but that just means it is conducting the heat away from the CPU or GPU
(In fact, from a medical point of view it is not advisable to have a hot laptop in your lap for very long, especially if you are a man
)