We just added the King Sling knot to our selection of loop knots in the fishng knot section. At last count, that makes at least seven ways of tying a loop at the end of your line we demonstrate on this site - either with a lure or as an open loop.
The theory of tying your lure or fly on with a loop knot instead of tight to the knot and line is that the loop allows for more natural movement of the lure or fly. There may be some truth to that, although there is the trade off in strength as no loop knot equals the Palomar or some other terminal knots in strength. The King Sling comes pretty close though. The King Sling offers a very easy way to tie a loop at the end of your line and it has a reputation of being stronger than the others. Give it a try and it may become your new g-to loop knot.