Two uses, one to keep excess rope off the bottom and avoid hanging down on rough bottom. When used for this they are tied onto the mainline with a short strap so it will go through the block and hauler, at a third of the way up from the trap, or so. The other use is at the surface ahead of the bouy to provide some slack rope in areas with alot of tide, tied on the same way with a strap a couple of fathoms from the bouy. This takes alot of strain of the old back.
Thanks for that explaination, i kinda thought thats why they used them. It must be fun running around gear and buoys if you don't have a cage on the boat with all those toggles under water !! I use a toggle on my shrimp gear most of the time, only problem is the sea otters like to chew on the toggles !! That bouy is in aprox 100 fathoms there.