How much does the gun weigh?
SAWC: Size and Weight Constraints. This is about how easy it is to carry something, in terms of how easy it is to fit in a pack or carry on a sling and how heavy it is. There is an economy on size and weight - you can only fit so many things on your person and you can only carry so much weight.
People are all over the place on this topic. Some will say you just got to lift more weights and others will go for lightweight options because that's what they heard was cool on some forum. The truth is: size (and weight) matters.
If you will never carry the gun out of your house, except to go to the range with it and shoot it from a bench, you may not understand how important this is. What I can tell you for certain is that if you have to carry a gun and ammo and other gear for long distances, the size and weight matter. Every ounce you save is more bullets or more water you can carry. This is true if you're carrying guns and equipment to a spot to hunt from, if you're a survivalist training for WROL, or making your way through the hills and mountains of Afghanistan. Though I am not prior military myself, any friends of mine that have been military and any current/former military reading this can certainly tell you that carrying the ammo, the armor, the water, and other supplies adds up and it makes it difficult to travel on foot over long distances. (And, that is true of people that are in tremendous shape!) A few ounces here and there turn into pounds and then the pounds add up too. It weighs you down, slows you down, and wears you out. That adds up to you being less effective when your life depends on your ability to act. Why carry an 7.9 lb Tavor when a 5.8 lb BCM AR 15 will do the job equally well?
When you read somewhere on this site that something is too heavy or too difficult to carry, it's not that I can't lift it or never heard of gloves or products like Talon grips. It's that the weight compared to other things that do the same job is just too high to justify using it over those other weapons, parts, etc. SAWC are critical for real-world use of weapons.