In the end, the decision to restrict line length is a philosophical one. From a design standpoint, a measure that is comfortable for reading is good practice. But a fundamental principle of the web is that users should be able to structure their own view. Users with a large monitor may not want their text blocks circumscribed if it means that a large portion of their screen goes unused. A low-vision user with fonts set large will not appreciate being forced to view long pages with short lines of text. So although leaving text free to fill the browser window may affect readability, following conventions may also affect the accessibility and legibility of your documents