Sometimes. editing is like being a detective. A sentence can be "technically" correct, but it doesn't "sound" right, it doesn't flow well as you read it. And if the sentence is grammatically correct, should you make a change to improve the sentence, and perhaps improve the paragraph as a whole? Or is this the author's voice, and you, as the editor, need to leave it alone?

Usually, it's best to make this sort of "correction" as a comment - thus leaving the decision up to the author. Perhaps the sentence was a mistake, and they didn't see the form it could have taken. It may in fact be the way they write, but they are open to suggestions for improvement. Or, this may be their preference, and they'll reject your suggestion. And that's fine too!

I think of editing more as a "conversation" with the author -- and try not to use the delete key quite so much. Most of the publishers I contract with have the utmost respect for an author's voice...l have come to believe that should be paramount in every project I undertake.