Defining commercial equivalents into two separate stages

Why is it preferable to separate need identification and specification or defining commercial equivalents into two separate stages?
Why is early supply/supplier involvement (ESI) important?
What are the disadvantages of specifying by performance? What are the advantages?
How does a supply professional know that a certain requirement is strategic?
Submit to your instructor your two to three page Word document (not including the title and reference pages). Your paper should be formatted according to APA style as outlined in the approved APA style guide, and should cite at least two scholarly sources in addition to the textbook.