I expect to take a little abuse from this post, but the greenland paddle people may be amused. Anyway think of this:
The main reason given for feathering is wind resistance against the raised end of the paddle. In a light wind, the effect especially with very small amounts of feather is not great. Can you really notice? With larger amounts (less than 90 degrees) and stronger winds, you can probably notice.
The other factor to consider is that the wind produces forces in other directions on a feathered paddle. Going into the wind, the force is upward on one side on the boat, and downward on the other in going into the wind or down wind. With a side wind, the force is forward on one side of the boat, and aft on the other.
Those who feather, tend to look down on those with euro paddles that do not feather as Newbies. Strange, they do not apply that to GP paddlers.
My conclusion is those who feather do it for other reasons. One reason being their wrists are more comfortable at different angles when pushing or pulling, or because they think it makes them look cool.