None, how many turkeys have you seen carrying around a can on an arrow? How many turkeys have you seen that dont move their heads at all? How many turkeys have you seen carrying a can and an arrow, and not moving their heads at all?

The point is a 10" circle is a better representation of your actual pattern than a can on an arrow. With the can all you get is how many pellets hit the can or the arrow. With the paper you see what kind of a pattern you are getting and what kind of pattern you can get if your poi/poa is off. It also allows you to establish your maximum range since once again you can see what your pattern is doing at that range.