If you notice what you think is an error in the answer of a person?
That depends. An opinion that differs from my own, Id leave it be. I might even upvote it, if its well expressed. A fact that I can see is a simple and honest omission, or mistake Id leave a comment, and remove the comment once they changed, or explained it. I dont think Id bother with a message if it was just one answer. Comments dont need to be permanent. However, if the error is a simple grammatical, typographic, or spelling mistake, Id use the Suggest Edits option.