Oh no Sona, it's no different than using 3 pans, and way cheaper, that plus the veg is crisper,
in the bottom I put say potato's and carrot, in the first tier cabbage and leek, and the top tier spinach or bok choi.
make sure the bottom pan is full of water, bring to the boil and cook for the normal cooking time. It's that simple really.
I tend to keep the remaining water and use that as the base for a stew.