The scanning will not degrade system performance. This is the most important consideration when establishing vulnerability scanning on critical IT infrastructure, because any degradation of system performance could affect the availability, reliability, and functionality of the IT services that depend on the infrastructure. Scanning during non-peak hours (A) could reduce the impact of scanning on system performance, but it does not guarantee that the scanning will not cause any degradation. Scanning followed by penetration testing (B) could provide more in-depth information about the vulnerabilities and their exploitability, but it does not address the potential impact of scanning on system performance. Scanning cost- effectiveness is a relevant factor for choosing a scanning service or tool, but it is not as important as ensuring that the scanning will not compromise the system performance.
Reference: CISA Vulnerability Scanning, Description.