This seems to be a point of contention - there have been posts about moving it to the right, moving it to the left, and about removing it entirely.
Moving it to the right would give the actual content more focus. As of right now, on the 13" Macbook Pro, 40% of the page (approximately 600px when the screen width is only 1440px, adjusted for retina scaling) is taken up with navigation, all on the left side.
Allowing the ToC to be moved to the right would drop that to 20% on each side, making the content the focus rather than the navigation.
In previous requests I saw that this was planned to be resolved in 2.2 which was a few months ago. I see that there's a place in the admin for this, but it would be nice to know if this is still planned.