We put a small amount of toe in on our boats, the reason we do this is that when you are sailing upwind, you will usually have an amount of weatherhelm, and so the rudders are travelling through the water pointing slightly to weather. If you have parallel rudders, and fly a hull, the windward rudder comes out, then when it re-enters the water it is not travelling straight, the result is usually that the rudder stalls, if have have a degree of toe-in this stops this.

regards

john p