What's the reason of this statement? "Content is usually best served by appearing as far left as reasonably possible"

I was reading "Ordering Disorder" Grid principles of Web design from Khoi Vinh, in where he mentions that without much explanation.

He got a long copy (8 units wide) inside a column of 10 units, in where originally he was using the most left unit as a left margin and the most left as a right margin. He moved the copy to the beginning of the most left unit, leaving 2 empty units at the far right for the reason of leaving it as far left as possible.

The original idea looks fine for me, with balanced space at both sides. Here how it looks. And the final idea here

Why exactly?