And for the Beatles probably a necessity to listen to various takes of stuff at home or even for their demo takes.
They were know for taking demos home all the time, they each had a tape machine at home (except maybe Ringo). This habit gave us the backwards vocals on "Rain", among other things:
From an interview in 1980: "I got home from the studio and I was stoned out of my mind on
marijuana and, as I usually do, I listened to what I'd recorded that day. Somehow I got it on backwards and I sat there, transfixed, with the earphones on, with a big hash joint. I ran in the next day and said, 'I know what to do with it, I know ... Listen to this!' So I made them all play it backwards. The fade is me actually singing backwards with the guitars going backwards. [Singing backwards] Sharethsmnowthsmeaness ... [Laughter] That one was the gift of God, of
Jah, actually, the god of marijuana, right? So Jah gave me that one!".
walrus