Perspective...
Economically tankering saves money if flying same route on same day compared to non-tankering flight.
Environmentally missions are re reduced as shortcuts are given, no holding delays are expected and less weight is carried.
When compared, on an average EU flight distance of 600nm (according to Eurocontrol document):
Economically: tankering saves 167 liters ~ £92
The economic impact above is equivalent to 4 minutes delay, eg once around the holding pattern, being second for approach on arrival at destination, speeding up and/or 20 extra track miles delaying please.