Youtube and Google Plus have changed their layouts such that in a very wide browser window, the content columns are left-aliged, leaving a large white space on the right side. This is a change from sites like this one, where content columns are center-aligned within the browser window.
I would like to know the reason behind putting web content on the left side like youtube and google plus did. I know they did not do that just for fun; they must have some reasons? Since I remember web layout was middle centered, why is this starting to change?