When a decision is made on a document (approval, changes required, rejected) all may be accompanied with comments. When an email is sent based on the decision, the comments do not accompany the email. If I'm approving a document and say approved but comment to my staff something like "This look great. Please ensure that you copy me when you send this to the client.", they aren't seeing the comment.
If I'm on the receiving end, I'm simply just seeing an "approval" and would just go head and send. I would not be going back into a project to see if there were any comments just in case.
