What is the primary purpose of defining secondary metrics in an optimization activity?

What is the primary purpose of profile scripts in Adobe Target?

Which variable has the greatest impact on the sample size required for a test?

A practitioner wants to test whether displaying user reviews on product pages improves conversions. The test audience includes visitors who viewed a product detail page in the last 7 days.
What is the primary metric for this test?

A campaign designed to improve newsletter signups has underperformed. Upon review, it was found that the call-to-action (CTA) text was unclear.
How should the test hypothesis be updated?