Unless your power is to control fire, the power to create fire or engulf yourself in fire would be mostly useless. Finding or making fireproof (not fire resistant) clothing would be a pain and uncomfortable to wear all the time. Plus, a lot of things are flammable, so unless you plan to be a super villain you're more of a menace shooting flames everywhere than you are a hero.
Mr. Impossible kept him alive in a vacuum to prevent Cody the human torch from bursting into flames.... until he became evil and trapped him in an oxygen rich chamber to power his skyscraper.