Everyone loves fire in fantasy and superhero fiction. It’s bright, it’s flashy, it’s explosive. It’s also a nightmare if Reality Ensues, because burns in Real Life are horrific. Meaning fiction that edges toward the harder scale of physics tends to play up the horror, or avoid having good characters use fire at all.
Which means the full potential of fire is vastly underused.
Because someone with a fine control of fire and heat ought to be grabbed by either potters, smiths, or – and this is the one that doesn’t show up nearly enough – the closest healing organization, stat.
A little physiology here. Two of the major threats to almost any organism’s health are microbial infection, and fungal infection. The cooler your body temperature runs, the more likely you are to be prone to both of those. This is one of the reasons you run a fever when sick; your body is raising the ambient temperature, betting on cooking the invader before it cooks the rest of you. Or at least weakening the nasty enough for the rest of your immune system to clear it out.
This also holds for a lot of homoeothermic (“cold-blooded”) critters as well. They just use outside conditions to raise their temperature, when they can. Alligators in particular are known for giving themselves “behavioral fevers” – basking until their temperature is significantly over its regular degree, and keeping it there.
The problem, of course, being the brain, and after that other vital organs. There’s only so long you can run at high temps without doing them serious damage. And this is where the control of heat would come in. If your character can give the rest of the body a fever but keep the brain cool-
Healers would snap that up. Seriously. Especially if you’re in a world lacking antibiotics, this would be a way to treat illness when nothing else works.
Infections. Abscesses. Stopped-up lymph nodes. Other injuries, where a gentle rise in temperature could help ward off infection. Cancer; people are doing work with that today, finding ways to target specific cells with infrared and leave healthy tissue alone. Unwanted magical growths. All of these and more would benefit from someone who can control elemental fire.
Of course it’d have its own set of side effects, and people are likely to feel much sicker before they feel better. Lymph nodes in particular; if you apply gentle heat to start getting the bacteria and toxins moving so your body can kill them and flush them out… well, you now have a rush of formerly stopped-up toxins in your system and the world’s likely to go spinny. And nauseous. Or worse.
And this is where you’d need people with other healing skills, if only on the level of, “give this poor soul ginger water to keep them hydrated”.
Fire is life. Think about how to use it!