Comment by ChrisMarshallNY

Sorry if your reply got dinged (looks all right to me, now). It was spot-on.

I think of "Yak-Shaving" as working on peripheral aspects of the project, to the detriment of the main path. Easy to justify, as they are "working on the project," but maybe not helping to significantly advance it.

I think of "Bikeshedding" as working on another aspect of the project (or a completely different project), because we want to (often, because it is more approachable or pleasant). This often becomes a problem, when the project is getting near shipping, as there's a ton of really boring stuff that needs to be done.

"Perfecting," on the other hand, can look like either of the above, but is, indeed, working on the main path, and advancing the project; just maybe not quickly.