I'm certain this isn't how they think of it, but when I see someone blocking traffic while they painfully back into a spot, I imagine them imagining themselves having to fly out of there without a moment to spare, like they plan on having a drastic emergency before they leave. And if that person isn't driving a police or fire department car or the like, I roll my eyes at the delusion of grandeur.
You are able to one-shot reverse parallel park into a much narrower gap without hitting the bumpers of the cars around you or getting onto the pavement.
However I always park with the front to the exit, since I might find myself in a situation where I have to drive away very quickly.
It might be anything from a dumpster truck about to block the street to some kind of family emergency.
I have the 20 seconds now but I can't be sure I will have them in the morning.
I'm not saying _I_ back into spaces. I generally drive into spots and reverse out of them. However, I admit that what I do is a tradeoff where I take on risk in order to have a mechanically easier time entering and exiting the space.
With cramped parking spaces, your real options are (a) backing into it or (b) driving forward into it. When you need to have a 90 degree turn, option (a) gives you more control over the eventual position of your car, and is frequently the only option.