I worked for a 'Major' for many years. We always had a box on the flight plan - be it PLOG or Computer Generated - which demanded "Reason for Extra Fuel....".
The closer I moved to retirement, so the need for extra fuel - for some inexplicable reason - seemed to increase. However, I followed the advice of an old skipper from years back who told me always to take what I wanted and put "PoM" in the box. It worked till the day I didn't.