At bare minimum, when you're folding a dirty diaper, you have to make sure the contents don't escape. Once that's done, though, there's a universe of artistic and aerodynamic expression available to you, as Kevin demonstrates in his recent post, Diaper Origami.
Around our house, my wife tends to make diapers into small squares, like giant raviolis, while I usually end up with triangular ones that ressemble giant versions of those paper footballs you used to flick between your deskmate's finger goalposts. As with so many things in life, the key is practice.
Diaper Origami [webgoonies]