Remember that when you agree with something another user has written, you are putting your own reputation behind it.

Consider the following:

• If it's homework feedback, does it address each section of the lesson/challenge, or only briefly touch upon one or two exercises?
• Does it provide clearly defined next steps for the student to follow?
• Have you read through it thoroughly, or are you simply agreeing so the student earns a superficial badge?
• Replies you agree with will be visible in your sketchbook

Agreeing blindly just to be nice is a good way to get your permissions associated with this function revoked, so make sure that you genuinely feel that the response is beneficial to the student.