To answer some q's
2.5 tonne in 737 is not much. Approx 60 mins. 1 missed approached and recircuit and you're at legal mins.
Bn-ad. Per tonne of fuel carried extra it will use about 60kg. So 5t is 300kg= $350. Does not sound much but virgin do 3000 flights per wk ( from website) = 1 mil/wk. Not all would use 300kg but rough enough.
So it is a find balancing act b/w balancing commercial and safety considerations. Why we get paid the big bucks ;-)