Of course, there are trim cranks and extensions with a ratchet - but not everyone always has these to hand. Good advice is expensive, especially if you just want to trim quickly. With a small sling, you can use your harness hook as a trimming aid, for example. This can be done in seconds and without knots - and at the end, the sling disappears again as if by magic.
And this is how it's done:
Try it out!
By the way: A good extension also reduces the trimming forces. HERE there's a test of 51 models.