A friend of mine flew long haul for a major carrier. The chief pilot sent a note to all long haul captains that some were carrying excess fuel, and please to keep it down to no more than company recommendations. All but one did. The chief pilot had a quiet word with the chap who didn't, and thereafter he too followed the company line.
One day he arrived in the Heathrow vicinity from the US and was held. And held, to the point where he considered it wise to divert. He took his 747 to Birmingham.
On the ground he rang the chief pilot:
"Blogs here. I decided to take your advice regarding fuel and save the company the cost of tanking it around".
"Jolly good, very glad to hear it".
"Only problem is, as a result I'm at Birmingham instead of Heathrow. So we have several hundred pax to transport to Heathrow, and the aeroplane is out of position".
My friend wonders how much 'tanking' one would have to do to equal the cost to the airline of just that one diversion.