It comes down to the content. If form is to follow function, you have to make a judgement call depending on how your site is supposed to work. Sometimes, making the content flow to fill the page is a good idea, but typographically, it's generally a bad idea. Text can be difficult to read on the screen at the best of times, but reading really long lines can be a nightmare. The length of the line of text gives the reader a rhythm and for that to be able to move around at random would be bad news for a site that relies on written content.