The only beneficiary of fuel tankering is the airline. It doesn't lead to cheaper fares. A reduction in costs, does not lead to a reduction of fares- rather it leads to an increase in profit. Having said that, this Is pretty 'small beer', in the overall scheme of things.
By tankering it introduces competition to your fuel supply and ultimately price. If you categorically did not tanker your fuel supply would become a nice little monopoly market at your point of departure.