Thumbrules have exceptions.

My 27,000hr tailwheel instructor would also add:

Or when you can't rotate and climb in the available runway (happens here in Colorado)

or when you can't haul your airplane over the Continental Divide at this weight

or when your fuel tank ruptures during 9G maneuvers (happened to him in his acro plane).

Really it's very much like choosing your pack weight. If you go for a daytrip and are lugging 100 lb of just-in-case are you being efficient?

Same with hauling 5 hrs of fuel for a 2 hr flight. It costs to drag that weight to altitude.