Speaker toe in

I agree that proper toe-in is something determined by experimentation.  This is the case with ALL aspects of proper speaker placement in a room.  

As for a reason for extreme toe-in, this can be useful if you are attempting to widen the area that one can sit in and still have some stereo imaging.  With extreme toe-in, the listener who is pushed closer to the left speaker will now be on-axis with the right speaker and off-axis with respect to the left speaker.  That means that the closer proximity to the left speaker is somewhat compensated for by the more direct sound of the right speaker.  The opposite holds true for the listener closer to the right speaker.

It is simply wrong to state categorically that any particular degree of toe-in is optimal and anything else indicates some kind of problem.  All adjustments--placement, toe-in, rake angle (tilt back) are specific to a particular speaker model, room acoustics, placement of the speaker and listener, listener taste, etc.  

With most speakers and situations, the ideal degree of toe-in involves trade-offs.  With little or no toe-in, the soundstage will tend to be wide and open sounding, but, the center image might not be as strong and pin-point tight.  By increasing toe-in that center image will tend to get more pronounced, but, usually the trade-off is a woundstage that does not sound as expansive, or the listener does not feel quite as immersed in the soundfield.  The "right" toe-in is where the listener is most satisfied with the balance of trade-offs.