Q: Why do I need this if I can just hardcode it?
A: This provide more visibility on how system decide what plan is suitable for each customer. The product team or your boss will not keep asking you why this customer is suggested with certain plan
Q: Why do I need this if I can just use excel?
A: Excel may require you to write some script or API call, to get the latest data from server. If you can build this into the portal or the CMS that is used by the product team or your boss, life will be much easier for them. This also allows you to easily add more parameter, for your product team to configure the rules without involving tech team