A good mechanic can do it without, I'll agree. Good mechanic = torque wrench or calibrated hand.
But I would never recommend someone do it without replacing the washer ($ 0.25). Oil pans are too expensive.
Don't you ever accuse me of being a good mechanic. I prefer lucky!!!
Seriously though, it is like the rear sprocket on the XX, I just don't replace them...until really worn or I have to.
Plus, I stopped doing it when I went to the Stealership, bought a washer, it was the wrong fucking one, took the other off already, had to drive back....just saves me the headache of dealing with jackoff's.
MaXX