I hope you and all of yours have a Happy and Healthy New Years!! Let's get back to guns....
Slings have several use and a few draw backs.
They are very useful for holding the gun near the ready position while your hands are busy with something else, like your fly, or water canteen. The shotgun is in position in more of less the same place every time. But….
A three point sling may interfere with reloading as one part of the sling is always near the gun. I’ve reloaded AR and shotgun with 3-point slings and sooner or later the sling gets in my way.
I like a 2-point sling on all my long guns. The sling is a distance from the operating control and still allows me to position the gun to the side if I need to transition to my handgun. Some 1-point slings are reported to alternate between slapping you between the legs and butt stroking your chin. Neither, as I see it, are desirable.
Most two or three point slings affect the mounted gun reload, just more weight and surfaces to catch wind and branches. I find the two point sling helps stabilizes the shotgun with the demounted reload.
Just make sure the sling has enough slack to reposition and rotate the gun. If not, the sling will bind, pull, hamper and frustrate you.