In regards to slings, there are those with experience that know the way things work and there are those without experience that make decisions based on peer pressure or appearances. Slings are to a carbine as holsters are to a handgun. Slings are a needed piece of equipment.
There are essentally three main types of slings (five if you count Chalker and Hybrids). Three point, two point, and single point slings.
Three points are unnecessarily complex. They provide a greater degree of retention and control compared to a single point. The extra lengths of strap can get in the way of basic weapon controls. Locking the gun down is not possible nor is adjustment on the fly. Transitions are not affected by a three point.
Single points allow much more free movement at the expense of control and retention. Switching shoulders is an easier task with single points. Transitions are problematic due to how they fall. Lack of control of the weapon with hands on, medical applications, using flashbangs, dragging wounded, etc is less than optimal.
Two points (preferably adjustable) allow for easier transitions. The ability to cinch the weapon to your body for hands on tasks is beneficial. The adjustable ability of the two point provides further stability in braced positions. Retention of the weapon is superior to single point. Donning and doffing is easier due to the ability to adjust the sling. Switching shoulders is viable by putting the sling only around your neck.
The most common defense I hear for three points typically goes along the lines of this is all I have ever known… because who uses those anymore anyway?
The most common defense I hear for single points is they are superior in vehicle operations – this is incorrect. In vehicle operations (4 door, van, SUV) it is the best practice to not have the weapon slung. It creates a snag hazard or worse if trying to exit quickly or be extricated.
One more thing, elasticity does not belong on any type of sling. It reduces the ability to secure the weapon to the body or use it in a braced firing position. Elasticity has the potential of causing negligent discharges when the weapon is slung due to the unwanted movement elastic provides.
Analyze your needs and be objective. Choose the option that suits your needs the best.