It is a mixed bag. When reading excessively long lines of text, it becomes difficult to locate the next line after completing one. Allowing lines of text to become too long is considered poor typography for this reason. When the lines are constrained to a reasonable length, the text becomes easier to read. Think about a page from a novel, or a sheet of A4 paper. They are shaped like that for a reason. Of course, images and video are another story. Constraining the size of an image or video with such wide margins does nothing to aid visibility.