For me, it's some of both. Flow is spectacularly useful when I'm working on a chunk of something and have a pretty good understanding of what needs to be done

For me, it's some of both. Flow is spectacularly useful when I'm working on a chunk of something and have a pretty good understanding of what needs to be done and how. The times when I'm contemplating dramatically different alternatives don't really lend themselves to flow. And in fact, I find that one of the things that blocks flow for me is a semi-conscious realization that I might be following the wrong path in some way.