A rule I've tried to follow in writing checklists and manuals (I suspect I've written less than my learned friend DAR, but still quite a few) is that if not knowing, or following something can cause damage to an aeroplane, or worse, risk to life. But if poor airmanship or an omission will only embarrass the pilot - that's their problem.
Hence my checklists would never, for example, omit engine checks, but don't include setting the transponder before take-off.
G