A firewall between internal network segments improves security and reduces risk by inspecting all traffic flowing between network segments and applying security policies. This will prevent unauthorized or malicious access, data leakage, or network attacks from compromising the network resources or data. Logging all packets passing through network segments may provide audit trails and evidence, but not prevent or mitigate security incidents. Monitoring and reporting on sessions between network participants may help to identify anomalous or suspicious activities, but not block or filter them. Ensuring all connecting systems have appropriate security controls enabled may enhance the overall network security posture, but not isolate or segregate different network segments. References: Info Technology & Systems Resources | COBIT, Risk, Governance ... - ISACA, section "Book COBIT 2019 Design Guide: Designing an Information and Technology Governance Solution | Digital | English"

The business case for an information system investment is a document that provides the rationale and justification for the investment, based on the expected costs, benefits, risks, and impacts of the project12. The business case should be available for review until the benefits have been fully realized, because it serves as a baseline for measuring the actual performance and outcomes of the project against the planned ones34. This helps to evaluate the success and value of the investment, and to identify any gaps or issues that need to be addressed5.
References
1: The Business Case for Security - CISA
2: Beyond the Business Case: New Approaches to IT Investment
3: #HowTo: Build a Business Case for Cybersecurity Investment
4: ISACA CISA Certified Information Systems Auditor Exam ... - PUPUWEB
5: The Business Case for Security | CISA