Man I have gotten pretty good at the ole bra thing(same style on the same woman for 20 years will do that I guess). I will just pop it while she is cooking or doing something around the house, it's pretty funny to me but less for her I assume due to the fussing.
It prevents the fibers in the rope from getting crushed right there at the link, making them weaker. It is a wear point once it gets dirty and grit start chewing away at it. I have never seen synthetic rope used without one. You do not need it for wire rope so maybe the PO didn't think about it?