I have found this link to be invaluable:
This eliminates the need to purchase an extension that does the same. It also appears to ignore certain portions of a website, such as a calendar which could go on infinitum. You ask what this has to do with SEO? The last thing you want on your site is a broken link. It shows an unprofessional site, one of the first signs of an amateur site, along with inconsistency of design. Yes, this affects your search engine optimization.