If you take off with full tanks every time then miscalculating the fuel is going to be difficult.
I think miscalculating fuel is difficult in any of our silly little spamcans. We all 'know' how many USGs or Ltrs or whatevers we burn per hour. Add a little for taxi and take off, diversion fuel, a little more (usually a fixed amount) for reserve plus a percentage of the reserve (say 10%).
This is basic stuff, and I'm not one to go on a trip and fill to the brim after every leg. If I can get there and back on full tanks then I will. Likewise if the fuel calculation is tight and I'm left in any doubt whatsoever, I'll uplift a drop or two to be sufficient.
you're now so heavy you won't make it off the short grass strip you're departing from...
I find that fuel/weight limitations arent too problematic in the UK with our temperate climate. Perhaps this would have more of an impact at high and hot strips. Mass and balance is usually the reason for dealing with fuel quantities in my experience. That's not to say that we shouldn't check performance figures every now and then, even just to make sure we can still do them!
