They act as a belt clip. They are disigned to fit Molle rigs or just slip over your belt. It frees you from having to purchase mag pouches, and more importantly has shaved roughly 3.5 tenths of a second of my mag changes. Your mags can sit 'munitions up' in your rig or on your belt so there is no need to flip them right side up. Less mag manipulation means less thinking and more rounds down range more quickly.
"...I would walk with my people if I could find them..."