I would suggest it has nothing to do with encryption or compression, but about caching.
At one extreme, you could transfer all data to the data before it starts to print. At the other, it would start to print as soon as the first bits arrived.
In the first case, accidentally kicking the cable out (or the wifi being corrupted by the neighbour's lawn mower, you lose nothing. In the second, you've trashed a print.
I'd think "off" is a poor choice unless you are in a big hurry and have a very good (wired) connection.