>> I think the primary thing that stereoscopic vision gives you is depth 
>> perception.
> 
>   The lack of depth perception of people who are blind on one eye has been
> greatly exaggerated. People with only one seeing eye have a surprisingly
> good depth perception.

Shut one eye. The world doesn't really look any different.

Now try and pick something up.

Oh. OK, my hand is actually nowhere near. I guess depth perception *is* 
important after all.

(Even more fun is trying to drive with one eye shut. I strongly 
recommend that you *never*, ever try this!)

On the other hand, if you're looking at a *moving* picture, you still 
have parallax to aid you. Not to mention that many types of surfaces 
have patterns that are predictable enough to allow you to guess how far 
away they are.

(It is notable, actually, that certain natural objects possess such 
scale-invarience that you can't reliably tell how big they are. Rocks 
work well in this regard...)

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