I don’t do enough of it, partly because it’s different in spinning and weaving than it is in knitting and crochet. I can’t really undo the work and use it in something else if I don’t like the way it’s working up. It’s not a huge waste if I’m spinning, but weaving is a lot time, and material, going by the boards.
When I’m spinning it’s pretty easy to see if the end is going to be worth the work. About the only time I sample is if I’m working to specification (i.e. a commission, or for a weaving project).
What I’m really thinking about is samples of made yarn; the idea is I make about an ounce of finished yarn. I can knock that out in a short chunk of time, and the opportunity to do things I’ve not been doing (high twist, linen, 3×3 cables, etc) will make me a better spinner (I’ll be doing more planning, designing, techniques) and I’ll have more records of how yarns went. I can snip a bit to have visual records.
I can also offer samples of yarn for purchase, so people don’t have to gamble 45-100 dollars; instead they can get enough to put some color into something for 15-25.