Nothing... except the prescribed 8 hour+ time it takes to make them (talk about delayed gratification)... I'm not sure why Ms. Joanna Chang wants you to refrigerate the dough for minimum 6 hours (develop the flavor, I'm thinking) but we did away with that step.
We'd never made yeast doughnuts before, so I'm not positive that our dough (stiff and on the heavy side) was the right consistency.
There are few things as satisfying as working with yeasty dough. I love the texture- the elasticity and poofiness- and the smells of the yeast. The Daughter likened the line-up to an army of puff balls.