irecovery get's your phone out of dfu mode if phone always starts in dfu mode
tested many times when downgrading firmware etc. ex if you get error 16** in itunes.
irecovery will fix the last part and bring phone to life again.
error 16** means restore is done, but something in the end was wrong.
i think it was something like that, but can be wrong.
setenv, i think have something do do with boot parameters.
like when playing with some sat recivers you can edit alot from there
but havent tested on iphone, dont want to **** it up
b.r