Field Control in SPRO

Hello, experts! I'm new to SAP SRM and I encountered a problem that the value of one new custom field I added to a structure cannot be displayed. But it is solved by adding an entry through 'SPRO -> SAP Reference IMG -> SAP Implementation Guide -> SAP Supplier Relationship Management -> SRM Server -> Cross-Application Basic Settings -> Extensions and Field Control (Personalization) -> Configure Field Control -> Configure Control for Fields on Item Level -> Metadata for Fields on Item Level'. The search path is as below.

The selected entry is the one I added. This method is taught by my leader. And I was excited but confused when the problem was solved. So could you tell me why I should add this entry and what the function of t-code SPRO is? Appreciate for your help!