My internal definition is something close to "7-steps removed"; yak-shaving is yak-shaving when you end up pretty far from the problem itself; whether its actua

My internal definition is something close to "7-steps removed"; yak-shaving is yak-shaving when you end up pretty far from the problem itself; whether its actually good or required is independent, just the fact that it might be time to start wondering if you went on too many tangents. Eg quintessential example of knuth -- everything he did was good work, and in the end useful for his overarching goals... but at some point in the middle of that situation its time to start wondering if he's gone off the deep end. Whether you decide yes or no, it doesn't matter, you're still deep in yak territory