What are the practical applications of "Charles' Law"? To whom is it relevant?

Have you ever seen those guys that inflate the long sausage-shaped balloons, and can twist them and fold them to make swords, and hats, and rabbits, and ostriches, etc...I try to do a bit of balloon folding in my A2 class, and at least I can do $s {p}_{3}$ orbitals...