John Mueller from Google has said blog comment removal can create an adverse effect on the website. It is an advice that has been given during the Google Search Central SEO hangout on 5th February.
One of the site owners has submitted a question to ask whether blog comment is a factor for search engine ranking. Some of the owners have wanted to remove blog comments. However, they do not like to hamper their SEO ranking.
Giving answer to this question, it has been said that comments are indeed used as a search engine ranking factor. Removal of the comment is not possible without its impact on the search ranking. To know more, you should read further.

Recommendation has not been made by Mueller at all on the occasion about the removal of comments. It is a decision that should be made by the site owner.
However, Mueller has given some details that may help the site owner to make a decision regarding removal of comments. It is important for a site owner to be aware about the response of Google upon viewing comments on your website. It is often looked as a part of content. In case a comment comes with information that may help the users then it can also help the site to get better search result.

Sometime, content becomes a valuable component of a page as it delivers addition information to the users that may not be included within the main content. However, it is not an everyday scenario. Sometime, content may not carry any value at all.
Looking at the queries on the website, it may be possible to detect effect of removing comment within a website. Information on the comment section may able to assist the searchers in better manner. Based on the impact, best possible action can be taken.

In case the comment is deleted then it can definitely bring some changes in to search engine ranking. Therefore, it is better not to delete the comment blindly. Instead, site owner can pick and choose comment that may help them with the search engine ranking.