I've seen people do that in real life.
You're right in that it's very divisive: about half of my buddies preferred the old parade-style sling
, and the other half liked the three point. Me personally, I preferred the three point, since it requires less handling on your part: with the parade sling, you have to pretty much be holding onto it the entire time. With the three point, you can let go off your rifle and it would just chill there next to you.
It's STRONGLY ADVISED you do not let go off your rifle, but there are situations where it's a good idea, like pulling your sidearm out when you run out of ammo, for example (also, I've always been a fantasy nerd, so I liked to let it hang at my side/on my back and pretend it was a sword in a scabbard. Don't do that, either.)
The parade sling is a lot tighter, and offers less room for customization when it comes to slack. The three points offers a lot more freedom with that (you can even tighten it as tight as a parade sling, if you wanted to).
But yeah, personally, I preferred the three point.