I've owned quite a few power washers of different spec, hot/cold/big/small/etc. Whoever said that you need to match the machine to the job above has it right. I've seen machines that would not do the job at hand because they were too weak and I've seen people do enormous damage with machines that were too powerful. An example would be someone destroying a smooth cement floor, (actually lifting the top finish), but there are many others involving wood and other materials.
For automotive or other greasy industrial applications, heat is a force multiplier to pressure but the machines are several times more expensive for a given PSI rating. For general household use, (decks/siding/driveways), cold is the way to go. For automotive use, you want relatively low pressure with heat. For things like door jam/hinge areas, you need a tiny sprayer that you can control the overspray of.
Here is my current hot machine, 1500psi electric motor with diesel-fired furnace:
I also have a couple of these little tiny ones around that I haven't gotten around to using yet:
