#1... Feathers do not flap in the wind like plastic vanes do when the arrow is flying..
#2... Feathers are a hundred times lighter than vanes which equates to more speed than vanes and also the rear of the shaft will stabilize faster because of the less weight.
#3... Feathers do not wrinkle up like vanes do. If you fuzz up feathers they will still provide you will all the control they always did.
#4... Feathers have hundreds of little wings that catch air and provide more control.
#5... Feathers fold out of the way if they should happen to hit something on their way to the target thus allowing the arrow to maintain its path better.
#6... They look a heck of a lot better than vanes do.

The only downside is that you do have to water proof them.