Mates Rates - Christ, dont try and use that logic on me if you ever fly with me!
The purpose of those words is more to cover the we predicted 15 kts and you got 10, or 25, NOT we stuck a tempo for TS on at 5pm local and it turned up at 6 am, so nah nah na nah nah its your fault.
I have no problems with interpreting TAFS and adjusting the fuel accordingly, in fact I do so all the time, I have often loaded TEMPO fuel on for an arrival that was scheduled a couple of hours before the forecast requirement and lo and behold the tempo came forward, but I have never, in more than 30 years of flying, including over 25 in command of multi crew aeroplanes, carried fuel for a requirement in the manner you describe.
It isnt practical on many aeroplanes and it isnt necessary, nor does it do anything to improve safety and it sure as hell isnt an economic thing to do.
It is my belief that our brief as pilots is the safe and efficient movement of aeroplanes and the people within - carrying fuel in the manner described satisfies neither of those elements in my opinion.
And I am not a "captain vapours" type person either before you have a crack at me.