ok, so i remembered this the other day, and also remembered that i wasn't %100 on usage etc.
the book says that the informal form of the imperative can be used idiomatically to mean 'if...'

eg:
будь я на твоем месте, я бы ушла от нее
if i were in your place, i would leave her
знай они, что...
if they knew that...

i haven't seen this construction come up before, so is it used often? are there any instances where it would be better to use this construction?

thanx