Having the knowledge of the subject matter definitely gives some advantage to an editor. However, that is just a superficial aid, because either way, the first requirement of editing is that that you have to read the text or content assuming yourself as end reader or a layman, who does not know anything about the subject he/she is reading. What matters is that the content should be grammatically correct, error free, coherent, well illustrated and consistent. As a reader-editor, you should not get stuck in between the text, while reading. In addition to the aforementioned factors, there are some other factors that prove that you need not to have the knowledge of subject matter you are editing.
Syllabus, in-house editing manual, style sheet, editorial board/team, both manual/hard copy and online references, spelling checkers, subject-matter experts in your editorial team, the EPR [Editorial Proof Reading] team, which will help in resolving any and every formatting issue, and last but not the least, you knowledge and wisdom are some of the major tools that will help you in the most critical editing of the subject that you may have not read at all.
Author is Subject-Matter Expert
The upcoming authors want to establish themselves as good authors. Therefore, while preparing the manuscript, they do not leave any margin for error, or plagiarism; rather, they always cite the books or the names of the websites that they refer to for writing their books. Therefore, it is rather easy to edit the books written by the upcoming authors. They do not mind numerous feedbacks and author queries, which an editor who does not have the knowledge of the subject, may raise. The same is the case with the already established authors, as they feel the heat of competition form the upcoming authors. Thus, they are doubly ready to work in accordance with the editor and take care of every query made in their content. However, as an editor, you may have to be cautious of instances in which you may overdo and make unnecessary queries. This may entail a demand from author to replace the editor working on his/ her subject. That will definitely not show any good on you part and damage the reputation of the publishing house. Therefore, you should not raise any query without reconfirming your doubt form some other source, e.g., Internet or the books on the same subject and syllabus published by other publishers.
The Danger of Making a Mess
If you have the knowledge of the subject matter, chances are that a situation may be created in which you may contradict some theory that the author may carry in the book, or you may loose concentration in editing, thinking that there could not be any error, whatsoever, in the content, or may overlook it once you pick up speed of editing the subject that you already know. On the other hand, if you have no knowledge of the subject that you are editing, you will certainly be doubly alert while editing so that you do not commit any fatal mistake, which in turn may earn you the author’s anger.
Therefore, not having the knowledge of the subject matter leaves you with a preconditioned mindset, which helps you in averting any type of error and thus brings good results and better products/ content/ books in the market.