Let's say I have provided an answer to some question, and then another user comes and provides a comment which looks something like:
"you should also add to your answer that X can often lead to Y"
And let's say I think it's a very useful comment, and I'm not really sure I need to add anything belong that "X can often lead to Y" part. Should I edit my answer to incorporate the comment, or should I just upvote it? The former makes my answer more complete, the latter makes sure credit is rightfully given to the commentator, which would have otherwise probably deleted her comment.
I also could incorporate it into my answer and credit the user by name. As Grace Note noted gracefully