A simple loop on a knife handle is for retaining your blade if it slips from your hand. The braided or looped kind is so you have some cordage along with your knife if you find yourself in a survival situation with no other supplies. Cordage is good for everything from food procurement to shelter building and firestarting.
As a custom maker I include a length of 550 cord with all my knives so the customer has the option.
_________________________
Anderson Knife & Tool, the cutting edge of innovation