As a cabinet maker, I haven't had the need to try it yet, but one use is as a press for gluing glulam (glued lamination) timber.
When making bent laminations (or even straight ones) the glued timber strips are placed in the former (or mould) and an old inner tube, cut near the valve and sealed at both ends, is placed in the former with the timber. The former is lightly clamped, or otherwise constrained, and then the tube is inflated to apply the pressure to the timber.
Ordinarily both halves of the former have to be a very precise fit to ensure an even pressure on the timber but for complex shapes that can be difficult to get right. Also for a one off, or short run, it may not be worth the effort to get both sides of the former exactly right.
So if an inner tube is added to provide the pressure in the former then only one side needs to be precise, the other side can be approximate as the inflated tube makes up the difference in fit.
Here is one using a fire hose to form skis.
http://skibuilders.com/howto/