Matt Cutts answers the question,
“Should webmasters use the disavow tool, even if it is believed that no penalty has been applied? For example, if we believe ‘Negative SEO’ has been attempted, or spammy sites we have contacted have not removed links.”
Have a question? Ask it in our Webmaster Help Forum:https://productforums.google.com/forum/#!forum/webmasters
Want your question to be answered on a video like this? Follow us on Twitter and look for an announcement when we take new questions: http://twitter.com/googlewmc
More videos: http://www.youtube.com/GoogleWebmaste…
Webmaster Central Blog: http://googlewebmastercentral.blogspot.com/
Webmaster Central: http://www.google.com/webmasters/