Agreed on the single point sling. Only useful if you're standing guard, and a regular 2-point sling can be used just as well for that purpose, which is to have it in ready position without needing hands on it. Slung over the shoulder crossways with the muzzle pointing down behind the back while walking. If you train at it you can have it ready to shoot from there in a quick second.
I learned the hard way to use a sling from hunting on public lands and scouting the day of the hunt. A lot of walking on those days and carrying a rifle or shotgun gets old quick if you don't have a sling. I also learned why my father preferred to hunt with a carbine. Much better for walking through thick brush and rough terrain. I'm sure that's also why the military prefers them.
I've found that slinging a rifle in the traditional way, barrel up on the dominant shoulder, enables it to be rotated up to the shoulder in a fraction of a second. Just my preference, I guess.
I am averse to slinging a rifle with the barrel pointing down, perhaps from hunting in snow where plugging the barrel with snow can have explosive consequences.