Sheet mulching

I'm being a bit of an internet magpie and collecting lots of info for my new allotment... and found some useful pages about sheet mulching. What's not clear to me is: do you mulch up an entire area and leave it for several months or a season or longer? Or do you plant through sheet mulch, so that the mulched area is productive during its period of breaking down underlying weeds etc? (Feel free to point me to links or earlier discussions about this)

Cheers
L