Here's a link to the OCF website called The Biopsy Report: A Patient's Guide.

http://www.oralcancerfoundation.org/discovery-diagnosis/detailed-biopsy.php

This is an excellent summary of the biopsy process and terms. In the Specimen Processing section more information is given on frozen sections.

As I understand this procedure, during surgery the pathologist will examine tissue as it is removed by the surgeon, and if they see suspect tissue they will continue to remove tissue until they get wide margins of healthy tissue. This seems to me that it is to the patient's benefit to have this done, and will help minimize the amount of tissue removed.

I hope this helps!