End Knots Overview
Introduction
In Japanese-inspired rope bondage, you'll most frequently see people use a simple overhand knot in the end of their rope. This is a tradition that seems to derive from historical use of low-quality and/or loose-laid ropes where the tension would easily become uneven between strands. When that happens, you have to re-lay the rope by hand from beginning to end, and when you get to the end, you'll need to undo the knot to realign the strands. So a simple knot that can be undone and redone makes that convenient.
The vast majority of people tying today will never perform that procedure. Most people who tie wouldn't even know how to do it. Nevertheless, end knots live on as the most popular option, I guess because everyone else is still doing it (or because the rope comes that way, certainly the lowest-effort option for suppliers).
The downside, of course, is that knots in the end catch when they are pulled through, a constant nuisance and something that happens no matter how good you are at handling the rope. I've seen people with decades of professional experience have their flow broken on stage by a stuck stopper knot.
Fancy End Knots
There are various end knots you can tie that have a much lower profile than the simple overhand. They are all still bulkier than a whipping, however, and because they're not easy to retie, they don't have the nominal advantage of overhand knots for loose-laid rope. The main advantage of these techniques is that you don't need any special supplies or equipment to perform them; there's also perhaps something to be said for the aesthetics of no foreign material used in the finishing.