Probably one of the more overlooked aspects of a setup. Here's an awesome tutorial on how precision washers work and why they are better than stock washers.
The first and most obvious benefit of using precision washers are that there are a variety of styles you can use to help enhance the way your bushings react to your movements.
Second one is simple. Precision washers just fit better on your kingpin. Stock washers often don't fit snuggly on your king pin, precision washers will.
Here are some options for precision washers that offer something a little different:
: Sleeved Washers :
Sleeved barrel washers allow the bushings to expand outwards but they still have the middle that extends the center part of the washer connected to the kingpin. This washer puts more pressure on the center of the bushing which gives it a snappy feel.
: Cupped Washers :
These washers hug the sides of your bushings which keeps them from squishing outwards when force is put on them. Ultimately it makes you more stable because the washer is preventing the bushing from deforming more.
: Flat Washers :
Flat washers are probably the most universal type of washers. They do what they need to do in a solid way, but it also allows you to stack washers if you have too much extra room on your trucks.