Well, a review campaign may help the project to enhance its functionality and remove any bugs found but I also think that review campaigns on bitcointalk help the ordinary end user like us to understand the project and decide whether to use it or not, based upon the opinions of people who review the service/product.
Sometimes these reviews also help as an in-depth tutorial on how to use the service and the pros and cons associated with it. If I wanted to use any product and it has a review campaign, I will always go through it before actually using the product.