What is a disavow tool? Disavow tool is the Google tool for disowning a back link pointing to your site with which you are not happy.
Now the next obvious question is Why does one has to use this tool ? Well the answer to this is that after all the updates which Google has done be it Panda, Penguin or Hummingbird lot of sites which earlier were giving out links have come under the preview of bad sites and it becomes very necessary to get these links removed from such site.
Now usually a person would say is that why does not one ask the webmaster to simply remove such links from their website. Here is when the problem arises; First problem is that the site owner is non contactable. He does not reply to any of the emails or the mail which is been sent to him gets bounced back. Second issue is that the webmaster or site owner is asking for an awful amount of money for removing the link. Yes donot be surprised this is very common practice these days. Not only asking money but a substantial amount of it as well. Third case is where the site has been abandoned and now there is noone who can be contacted for the removal. So in these cases how can the link be removed which is resulting in negative SEO for our website. Well here is when the disavow tool can be used.
Now it was been asked frequently by people that when should disavow tool be used ? Some people said that this should be used only in case you have got a written penalty for your website but recently Matt Cutts put an end to this debate and he said in his video that this tool can be used anytime when you feel that a certain link should not be in your back link profile. You donot need to wait for any warning or notice. When ever you are doing bad link profile analysis and feel that certain links are bad then you can use this tool to get that link removed from your back link profile if the webmaster or site owner is not responding.
So feel free to use this disavow tool without any worries and carry on with cleaning your bad links.