They can spot errors of your system configuration that have security implications, sometimes correcting them if the user wishes. Vulnerability assessment products allow consistent auditing and diagnosis of system configuration settings that might cause security problems. They can recognize when your system appears to be vulnerable to particular attacks. Vulnerability assessment products also allow the administrator of a system to quickly determine what attacks should be of concern. They are not magic bullets.
Security is a complex area with myriad possibilities and difficulties.
The time it takes for this to occur is also minuscule. There are no magic solutions to network security problems, and intrusion detection products are no exception to this rule. However, as part of a comprehensive security management they can play a vital role in protecting your systems. They cannot compensate for weak identification and authentication mechanisms. We must still rely on strong identification and authentication of users.