I first came across them via Austin Kleon who did a whole book of blackout poems and is my general go to author when I'm in a creating/marketing funk. He's sweary, he's very anti marketing speak and totally into Brian Eno's idea of scenius "genius is individual, scenius is communal."
I find them freeing, whenever I'm a bit stuck with artwork, or if a student was when I was teaching, my course of action is limitation. I get paralysed by indecision and wrapped up playing with technique or tools rather than getting an idea across effectively. So if I've got a line I want to make when I'm drawing someone and I have all my brushes, pens, inks, pencils etc out and I have no idea how best to describe it, I'll usually grab a twig out of the garden and try and use just that and ink, or splat something on the page to contrast against rather than having the scary possibilites of a blank page, it's like telling your brain it's ok to fuck up as you can blame the lack of tools, so you may as well experiment, which is the most important thing to me making in a satisfying way.