Can't beat the good old cheesewire when 2nd fixing on fixed price
what a mess
I have seen this done many times, and assumed it was how people had been taught. I always thought it was a dodgy practice to be straining the CPC like that.
As has been said, back boxes do not move, and there should not be any bare live conductors that could move and come into contact with it.
I once went to a job (installing the networking) where the sparky had left all the mains sockets in the floorboxes loose - screws in, but not tightened down. I just assumed he'd been "nice" in not tightening them down and possibly having them interfere with putting the data plates in, and so I just did the screws up as I fixed my plates in.
Next day there was no power in (some of ?) the floorboxes, and someone just flicked the MCB back on. After a while, someone managed to correlate the power going off with a pop from one of the floorboxes
Looked behind the power sockets to find there'd been a short between L&N where they'd been pressed together hard between back of the socket and the box
Sparky was called back, and he was indignant that I'd tightened the screws, turned out that he'd left the screws loose to avoid exactly that problem
I suggested to him that having the sockets move all the time wasn't a great idea - he genuinely thought that plugs would only be put in once and never again, I suggested that that was not the case (eg laptops, the cleaner's vacuum cleaner, ...) and he grudgingly went round and was more careful in routing the cables behind the sockets.
Over the years I've come across a few loose sockets that move around and the users seem to be completely oblivious to the potential risks