Optimizing your website takes both time and money. Effort is put into on-page optimization such as adjusting title tags and building content. Hours are spent building contacts and acquiring links from authorities in the industry. And after all of this work has been put into building a website that will rank for its keywords and start brining in revenue, owners forget things like basic maintenance.
By neglecting to maintain your website you are placing the rankings that you have worked so hard to obtain in jeopardy. Search engines are trying to produce results that lead to a good user experience. If a user types in 'Blue Widgets' and clicks on a website that is full of broken links, then their user experience will be poor. Broken links is a common and easily rectifiable maintenance issue that may be hurting a website.
If your website has a blog which is open for anyone to post comments on, you will want keep a close eye on it to prevent people from posting spam to unrelated topics such as 'diet pills' and 'Viagra'. External links that don't contain 'no follow' tags are basically seen by the search engine as an endorsement. The last thing that you want is for Google to think that you're endorsing a site to an unrelated 'bad neighborhood'.
Make sure that your site never goes offline. If your website is located on an unreliable server which frequently goes down you should find somewhere else to host it. This is obviously a no-brainer but many people forget that this will have a negative effect on their rankings. If search engine spiders visit your site and find that it periodically goes offline you will see this reflected in a drop in rankings.
It's easy to get to forget issues such as making sure that the link you put up three months ago is still pointing to a live website, but it's important to check. The last thing that you want is for your websites rankings to be held back from its full potential due to simple maintenance.