Very few in the commercial aviation sector, there are comprehensive rules governing fuel for flight planning so mistakes are not common. Those rules can vary a bit from country to country, but in the majority you need enough fuel to reach your destination (obviously) plus a percentage of that amount for missed approaches or delays, then an additional quantity for diversion to an alternate field plus extra again for missed approaches and delays and such. Many pilots like to add an additional buffer on top of all this too, though there are airlines out there that like to shave every cent they can from operational costs and will put pressure on pilots to be as economical as possible - this doesn't mean endangering anyone, just that compliance is reduced to the minimum required.