Guess I'm in the bowyers knot camp.
I've made double loop strings before but have a tough time keeping up with the string when not in use and I'm not a "string keeper" kinda guy. The one end secured allows me to hang my bows vertically on the rack with that 3 or 4 inches of slack on a peg, loop end up without the bow dropping through the string. Limited room that I have, many bows to hang.
Another advantage is when I get really lazy (which is most of the time), I can borrow a string from another bow even thou the length is a little smaller or longer and it will still work.
If you tie a timber hitch knot correctly it won't stretch or come loose. Now, if you only loop that string a couple times building that knot it just may. A bow with allot of reflex will remind you quickly on how to tie one. Can't tell you how I know this, but it may beat you up in the process.
One more advantage and I'll leave this alone, is that it looks cool with a little homemade string hanging from the end.