Used to fly in north of Spain a few decades ago, not much in the way of weather forecasting you could rely on. Luckily it was a shortish flight, so standard fuel for us used to be round-trip + 30 min, without having to leave anything behind. Several time left with a CAVOK NOSIG and after passing the marker, and getting transferred to tower hearing: "Fog just came in, its now VV000, and RVR0100, what are your intentions?". There is just no way you will ever recoup the cost of running out of fuel, by tankering less fuel if you are flying to isolated, single runway places with dodgy weather reporting.