When defining the interface for an extracted COBOL service, why should the interface be kept narrow and focused?

Think of it like working hands-on with IBM mainframe systems — the answer here is 'A narrow interface reduces the number of COPY statements needed in the COBOL calling program'. A narrow, focused interface minimizes the surface area between service and callers. Internal implementation changes do not force callers to change, enabling independent evolution of each service. On real mainframe exams, this concept comes up repeatedly so make sure you have it locked in.