I do a lot of designing and I spend a considerable amount of time swatching different stitch patterns. I’ve found that I like to spend time with a stitch pattern before I commit to a fiber, especially if it’s a luxury fiber like silk or cashmere. So, I keep a skein or two of orphan yarns in my stash and partial skeins.
Stylecraft Special Aran with Wool is a perfect yarn for this. You could buy one skein to make a couple small projects, then keep the rest to use for swatching. This way, I can spend some time with the stitch pattern and if I find that I do not like the process of creating it I don’t feel bad about wasting the yarn used.