I believe this 3 column design with a largely empty and unused first column is a massive waste of space, especially on technical sites that often use wide `code` segments that then needs to be sidescrolled to be fully read. Everything that's in there should be where it is now or in a burger menu (this appears to only happen on very narrow displays on SO).

But I am certain this has been mentioned and ignored before... 
(Edit: I've seen it will have at least a workaround in form of a preference. This should be the default to make the site more useful to anon visitors and casual users). 

<s>Other than that: Will the new layout have better support for the small mod box on the left side that disappears on narrow displays? If not: Why?</s> **This is solved now, even in the old theme :)**