A common scenario in industry is for the sales manager to stick his head around the marketing manager’s door and say “Now that we’ve got the Red Widget 2, I’d like all references to the original Red Widget removed from the website”, which leads to the marketing manager doing just that, by deleting the relevant pages.
This is a mistake for so many reasons. Never just delete pages. Firstly, you’d managed to get your original Red Widget page onto the first page of the Google results for “red widgets”. Now you’ve deleted the page, anybody clicking on that link will be led nowhere. Eventually Google will see that the page has gone, and your entry will be dropped completely (with your new Red Widget 2 equivalent page still only having worked its way up to page 7 of the Google results). Secondly, other sites (such as those running your press releases) will have linked to your original Red Widget page. Unlike Google, they don’t update their links, so those links will be broken forever, losing you potential visitors. Finally, Google “ranks” your site on the basis of how many other sites link to you. If the pages those sites link to are gone, you lose that “vote”, and it’s hard enough to get links, so don’t throw away ones you’ve already got.
So what can you do? The options are discussed in a 7-minute video called Whiteboard Friday – Expired Content on the SEOmoz website. It’s a clear and concise guide, and perhaps the only technical thing you need to know is that a ‘404’ is the page you get when the address you’ve typed in doesn’t exist, and a ‘301’ is an invisible redirection to a different page.