As with anything, they can be either, depending on the person. There are alwasy people trying to get the most out of any tool or object they use. They will tinker with car engines, flashlight drivers or computers. Some do it to get a better product, some do it to test their skills and some do it just to say, "hey look at this".

That said, the "professional" use of hot loads is to get better performance out of a gun/caliber, without going beyond the capabilities of either. If you can load up the powder in a 9mm, so that the performance is closer to that of a .45, (I'm using these two calibers for reference only, not saying one is better than the other) then you have achieved the ability to carry a more powerful round in a smaller package, allowing your gear to be more efficient. The SEALs have been able to do this. They carry a lot of ammunition. If they carry 1000 rounds of 9mm instead of 1000 rounds of .45, the weight they bear is reduced substantially. This is done in hunting and target shooting as well, although target shooting is more for performance than weight.

Hope this answers your question.