With the right kind of speakers (described in my post), not at all, except for the loss of the image broadening effect of early sidewall reflections. The soundstage width is normal, and the depth and sense of immersion in the acoustic space of the recording have been reported as better than normal. If desired, soundstage width can be increased by increasing the speaker spacing.
I get many questions about (and sometimes well-meaning offers to "fix") my speaker setup at audio shows. They are usually skeptical when I explain why my setup is correct for my speakers. Then I ask them to close their eyes and tell me whether they hear whatever problem they expected, and they never say they do. Then I ask them to sit in whichever chair is farthest from the centerline and tell me if they still hear a decent spread to the instruments. And they always say they do.
In my experience, intermediate amounts of toe-in usually do not work well. I would suggest either going all the way to axes criss-crossing in front of the center sweet spot (assuming you have suitable speakers), or just sticking with a normal configuration.
Duke