Bloke I know was a copper a long time ago.He and another bloke were being considered for 'traffic' at their pre assessment,they were out and about and the other bloke drove front first into a parking spot, my mate got the spot on the course.The perceived thinking is that the supermarket, to fill the boot is the time you drive into a space, to keep your boot accessible, is right.
There's a school of thought that driving into a space might deter a car thief, who has to start it and turn it round before he's spotte, but I don't see it. also if cold wet and very windy, nose to the wall keeps the elements out of the radiator. Reversing out of a space in cold or wet with a cold engine and less than 100% clear windows is harder than reversing into the space when they're warm and clear.
I can't remember where I read it. Wasn't my brother's Northumbria Special Patrol Group copy of Roadcraft by HMSO, which he lowned to me the day I passed my test in 72, or I'd not have got the lecture in 76.