Advice: "Sleep when the baby is sleeping" - how?

Right, just a couple of things, firstly how but:

~ if I do that who will stop the 3 year old from doing irreparable harm to herself, let alone fetch her snack after snack

~ if I do that how will there be a single dish left in the cupboard or clothes in the drawers

~ if I do that how will the bills get paid, shopping get ordered and put away, etc etc

I mean, what am I missing?