Do you always knit gauge swatches? Sometimes? Never? I usually do. Always if I care about the size of my finished object. Sometimes, like with the Xmas tree skirt I'm working on now, it just doesn't matter. The skirt starts in the center as a small circle (well, hexagon, actually) and keeps getting bigger. I'll stop when it's either big enough or I'm out of yarn.
I've been thinking about gauge today because I've been catching up on my knitting podcasts and several mentioned going up or down a needle size to get gauge to match a pattern. It surprises me that people do this. To me, the yarn determines the needle size. I'll often swatch with different needle sizes, but I do it to see what size gives me the drape and density I want for the knitted fabric.
I actually did swatch my tree skirt yarn to pick the right size needle. Mosaic knitting gives a denser fabric than stockinette and I want a fluffy, soft tree skirt, so I'm using a big needle. The Bernat Happy Holiday yarn recommends a US 7 needle on the ball band, but I'm using a US 10.5. I started swatching on a US 9, knowing I'd want a bigger needle for a mosaic pattern. I worked my way up to the US 10.5 before I was happy with the fabric density. If I had a US 11 I might have tried it, but the US 10.5 is giving me a nice fabric.
I just never would have thought to change needle size to get the same gauge as a pattern. I don't often knit from someone else's pattern. When I do, I determine what my gauge is using the needle size that gives me the density and drape of fabric I want the item to have. Then I do the math to adjust the pattern to my gauge. Sometimes you can just make the next size smaller or larger and not have to do much in the way of math. Sometimes I do end up with a lot of numbers handwritten into a pattern, but I'd rather do that than make something with a fabric that's stiff as a board or so loose the wind comes right through.