Unless I'm making something very small, I generally use my circs as flat. One reason is that I have the turbos, another BIG reason for me is that anytime I get up from the couch, one of my straight needles escapes down into the cracks. When I'm out in public, I don't worry about dropping one, or losing one, or forgetting to take one with me from home. I have lots of straights, because I've been knitting so long and it never occurred to me to use them all the time, but I find I'm heading in that direction.
If someone is just starting out, it saves the expense of having straights and circs in all sizes.
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