I worked for one company where the chief pilot would always request why extra fuel was carried...and it wasn't for about a year that I found out why he never did carry any extra.
Enroute between two SE asian rather large cities he climbed the aircraft to FL350, only to me told by ATC (via HF) to descend straightaway due to crossing traffic ahead...only option being FL280.
His actions were quite astonishingly simple on this occasion, he simply turned off the HF and continued to destination at FL350.
Simple as that. Wasn't the first time either, so I was told.
Now some might well not believe, but another Captain on the obs seat, as well as the duty F/O and F/E all had the same story.
I kid you not.