One of the reasons to invest in professional copyediting for your book is to publish a work that is as free of errors as possible. But what is an error, anyway? Who makes the rules, and what is the logic behind them?
Can it spot a cliché or catch a redundant phrase? Yes. Can it evaluate whether your syntax and diction are in line with other books in your genre? I think so. Can it predict whether your novel will be a bestseller or evaluate your story arc? Not yet.