Toe-in is a very interesting topic. I think when we toe-out we are editorializing the sound (presumably to taste) and there are tradeoffs. Assuming a speaker that wasn't designed to be toed out, with toe-out you're not hearing the speakers deliver all the high frequencies that were intended by the designer - the higher frequencies have very little dispersion and therefore are missing your ears and at best you're hearing only the reflected sound of these frequencies. This may be desirable but it is editorializing, whether to make up for an issue somewhere else or purposely change the character of the speaker.
It makes total sense to me that a speaker designer would want the speakers toed-in as it minimizes the unknown effect of side wall reflections.
I've noticed that with my Magico M-Pros, being off axis can result in some unpleasant high frequencies compared; if I have them toed-in as recommended the highs are much more natural and extended. The highs are not subtle or rolled off in any way of course, but one can only assume that's the intent of the designer. Having the speakers completely toed-out reduces the unpleasantness (practically eliminates it) and has some non-treble related effects that I enjoy but it certainly is a darker, less airy and less extended presentation.
I think this is truly a matter of taste and I imagine it would work better in rooms that don't have close sidewalls.