Just to add an oldie point of view, I had a stint at house bashing in the 70s the 1970s before some smart Alec jumps in with a comment.
Anyway I digress, the scenario went like this, one Electrician and about 5 or 6 Apprentices, once the Apprentices were shown what to do, some first fixing some 2nd fixing, my job as the Electrician was to oversee this shamble.
Not a lot can go wrong on repetition work, or so you would have thought, switches an sockets at the wrong height, how do I connect this 3 gang 2 way switch, and so on, someone mentioned speed and cost, it was the ethic in those days same as it is now, the trouble was and is still today lots of these Apprentices, qualified and became Electricians, only knowing new build house bashing, a sad reflection.