A 404 error occurs when someone requests a page that is not available on your site. The link to your page might be wrong, or perhaps the page has been moved. These errors can be particularly problematic when moving your site to a new domain. Spotting these errors is the first step. Google webmaster tools provide a handy link fo test your site for 404 errors, just click it and you should get a list of all the broken links on your site.

What do you do about these broken links? This depends on your site and on the importance of the page. If you have a large site, you may end up with thousands of these errors when you move domains. What’s more, more errors will creep in over time. You can, of course, use 301 redirects to fix them all, but that approach is not always practical.

• You may have hundreds of errors to fix, that can be very time consuming.
• Too many 301 redirects can slow your site down! Slow page loads will in turn affect your search engine rankings, an undesirable result.
• The broken links could be providing very little value. Not all links are equally useful, sometimes its best to just leave them broken!

Google’s site-crawling algorithm will eventually disregard broken links and they won’t be indexed. This is why you can just leave 404 errors on your site: If the page is not important it will get removed from google’s indexing automatically, you don’t need to do anything. A 404 error will not affect your site’s performance, while a 301 redirect can slow it down.

Having said that, there are some pages that you definitely want to redirect. If your page is getting good links from other sites or indexing well, you definitely want to keep it. Incoming links are good to have, you want to keep them wherever possible. If your page is an obscure one which doesn’t get indexed, it may be best to let it 404.