Its just a safety measure. Bolts have a tendency to vibrate loose so safety wiring them prevents that. As far as the extra washer comment.. What they were talking about was the rubber O ring that is already on your oil filter when you buy them. sometimes during an oil change, when you remove the filter, the rubber O ring will rip off the filter and stick to the engine. Then if your not paying attention, when you put the new oil filter on, you end up having 2 O rings on there and the magical leaks and oil sprays soon follow.