I can't speak for diN0bot of course, but the reason I work this way is to minimize distractions. I don't want all that stuff in my peripheral vision when I'm busy trying to get stuff done.
Personally, what I find worse than 'distractions' is being blinded by whitespace caused by Firefox (/whatever) being way too huge.
And, full-width emacs!? On my monitor (with a rather large font size) that's almost 250 columns, I hope you don't have any code over there! If you're vertically splitting emacs, then, I think we're on the same page. It's not about windows themselves being any specific size, it's about making them an appropriate size for their content.