Google’s link disavowal tool provides website owners with a way to inform Google that they don’t want certain links from external sites to be associated with their site. Links from external sites are used by Google to rank websites. The site may have paid for links in the past or may have participated in bad link networks. Both of these activities are against Google's guidelines and could lead to the site being penalised and removed from the Google listings.
In Webmaster tools (edit. now known as Search Console), site owners can proactively use the disavow tool to avoid a manual action. They can look at their existing link profile and identify if there are any sites which either themselves or a disreputable SEO agency have linked back from and disavow them.
What types of sites should be disavowed?
Examples of these types of bad sites include:
- Unnatural links
- Thin content with little or no added value
- Cloaking and/or sneaky redirects
- Pure spam
- Cloaked images
- Hidden text and/or keyword stuffing
Keeping ahead of the game
Links are one of the most well-known signals we use to order search results. By looking at the links between pages, Google can get a sense of which pages are reputable and important, and thus more likely to be relevant to searchers.
No one is certain how Google's algorithms will change in the future but one thing is sure. If you have links in your profile from spammy sites then they will come back to bite you at some point in the future. Better to take care of them now and disavow them before a manual action ensues.
Things to bear in mind before disavowing links
Before disavowing links it is worthwhile trying to get the link taken down. If you have created the link yourself, this should be relatively straightforward. Valid efforts need to be taken before submitting a disavow files otherwise your reconsideration request may be unsuccessful
If a domain has linked to you many times and you want to remove all links from that domain, you can use the "domain:" operator in the disavow file for convenience.
Also, make sure that you don't disavow organic links to your site. You don't want to undo the positive links that have been built up gradually over time.
If you're unsure whether to disavow or not then ask your local SEO company for assistance. They should be able to provide you with advice on this matter.