It's useful for when you need a loop and a secure knot that won't slip or become undone. Basically where you would do a regular knot but need more knot strength.

I've used it for securing crab pods, pulling out a small tree, hanging decorations from ceiling hooks, as the front anchor for strapping down things to the top of my car, connecting lines to kites and tying the tea bag string to the handle of my coworkers mug as a prank to name a few uses of the top of my head.

I've also used it for climbing in certain situations but I would highly recommend learning the figure 8 and using that for all climbing things related.