I have recently noticed a problem concerning to fuel tankering.
Tankering is supposed to be done in order to save costs, but sometimes produces just the opposite results.
An Airbus 320 flying from Rome to London in December doing tankering, will arrive with, lets say 14000 kg of fuel. At the time of the arrival that big amount of fuel will be at a temperature of -17ºC causing the usual London humidity to saturate on top of the upper wing surface in the form of frost. The exterior temperature in London will be very close to 0 or below. Even if you refuel some more tonns of fuel it will not heat enough the wings to melt the frost and you will have to deice before the next flight with the high costs and the delays involving deicing.
On the other side, if you arrive with 3 tonns and you refuel 14 tonns of fuel at a temperature of 6ºC you will easily warm the wing avoiding the deicing.