As was already said, a carbine on a single point sling is going to be dragging if you drop to a knee, have to climb, etc. I'm 5'7" and a single point on a carbine is not great for me. Maybe if I tried it on one of my sbrs i might change my mind... but i doubt it.
Worse than dragging - a single point sling WILL SLAM YOUR RIFLE INTO YOUR BALLS, eventually. not trying to be funny here, but this is something every guy should take into account.
Here's another though - if you use a single point sling - how are you going to wear the sling? Are you just going to loop it around your neck? I know one very good shooter who was paid to shoot people on the other side of the globe, then paid to teach other military folks how to do it, and now runs a successful shooting school - he really likes single point slings over his neck... Maybe it works for him, but if you use that setup and are down on the ground... what happens when somebody yanks your rifle? either they choke you or they pull it right over your head.
If you're putting one shoulder through to help secure it - why even bother with a single point?
I'm not tactical - but I cannot see the benefit to a single point sling over a 2-3 point for must guns. well, one benefit - it makes transitioning from strong side to weak side easier. maybe for a PDW it helps keep it tight and concealed, but I haven't tried taht yet.