Google’s Search Advocate, John Mueller answered a question regarding “what backlinks should be rejected and which ones should be ignored?” via his Twitter account.
The person asked a question, which went something like this:
All my clients get too many spam backlinks from Blogspot. So should we reject it (disavow) or will you guys (Google) handle this kind of thing automatically?
John Mueller then answered the question with a short answer:
The person then asked an additional question:
But how do we know which backlinks to reject (disavow) and which backlinks we can ignore?
John Mueller again answered:
Please follow the guidelines at https://support.google.com/webmasters/answer/2648487. Especially in the section related to manual actions.
Launching Google’s guide page we don’t need to disavow all links that we consider spam. Because Google’s system can automatically assess link quality and ignore spam links without us having to manually disavow them.
Disavow must be done if:
You should reject a backlink only if:
Your website has lots of spammy links, artificial links, or low-quality links pointing to your site. The link causes a manual action or is likely to cause a manual action on your site.
If we refer to the 2 points mentioned by Google, we don’t need to worry too much about spam backlinks that might be done by competitors, considering that Google’s system will automatically ignore links that are considered spam.
We only need to disavow if the links cause manual actions or have the potential to cause manual actions.