Q. My editor has added instances of the word that, and I thought it was best to avoid the word that unless it was integral to the sentence. In other words, if the sentence works without it, then leave it out. Am I right or not?
A. CMOS prefers to retain that, for clarity; please see section 6.27. Although there are times it can be safely omitted (QED), sometimes that is needed to keep the reader from stumbling: “He gently suggested the plan to escape by means of hang gliders was harebrained.” Unless you are certain how to judge each case, it might be best to trust your editor.