In most cases a settlement agreement is something that your attorney and the employer’s attorney have worked on. Therefore, you have someone with legal expertise assisting you and explaining the document to you.
A severance agreement, on the other hand, may be something that just comes out of the blue. You employer hands you these documents, provides minimal explanation, suggests you get an attorney, and tells you that you have thirty days or less to take it or leave it. Your next step should be to get an employment attorney to review the document and explain what you are getting and what you are giving up.
While many severance agreements are written with care, some employers, either on purpose or by accident, include things in a severance agreement that the employee should be aware of.