Exactly, as I am not particularly good at organising my time it's useful to find effective short cuts - especially to things that otherwise require the oven to be on for a long time.
Might try it next time I do a dauphinoise too - steam potatoes in microwave with a little milk, pour over cream, cheese on top, in the oven for 30 minutes and see what it looks like. I normally do a dauph for 90-120 minutes on a low temperature and that's a long time to have the oven on if I'm not doing other casserole type things at the same time.
Mind you it would probably cause much offence in France, so don't let them know what I'm up to with their cuisine