What does it actually cost to carry extra fuel all other being equal?
A quick look at our manuals, paper graphs, thick lines etc I get a figure of about 25kg extra burn per 1000kg heavier, less than a minute of average burn per hour.
So you get an extra 15 mins fuel with no alternate planned, cost to carry if you average 2 ton /hour = 500kg or on above figures 12.5 kg extra cost
In Europe you could need an extra 25 mins for a suitable divert so 10 mins more than the given 15 mins, call it an extra 15 mins to save the maths, another 12.5 kg cost.
I am sure we could all come up with instances where the company waste more than the 12.5kg cost of the fuel that would not cause my sphincter muscle to become irritable if they made the cost savings there!