Knitting is an expensive hobby. Designing knitwear might be even more so, at least in my case. Why? Because at least one skein of yarn is going towards just the swatches, meaning I have to make sure to purchase one more skein of yarn on top of the set amount. I'm quite particular about my swatches, since different yarns will produce different results. Once I swatched a lace/nupp design using wool-based fiber and it didn't work out at all. Then I swatched it on linen yarn and the results were remarkable.
Sometimes, however, when I am working on a design and I already have all the yarn I need for the project, I have to make extra swatches, apart from the standard stockinette swatch. The pattern I had envisioned to use for the project doesn't work well with the yarn and I can't simply just use a different yarn because... I have already invested quite a bit of money into the skeins. So I have to make changes and adjustments and use up just a bit more yarn until I have swatched a design that is to my satisfaction. Designing knitwear has taught me to be patient and flexible. I believe that the more I work with different yarns, fibers and weights, I'll be able to know which ones are best suited for different types of projects, like lace, cable, colorwork, accessories, garments and even seasonal knits.
Confession time: I actually enjoy swatching for garments (I never swatch for accessories unless it is to test a pattern), since the information I gain from them is rather invaluable - gauge, how it reacts to blocking, drapiness of the fabric, etc. It's just a part of the process of designing!