A network-based IDS inserts an appliance into the network, through which all traffic is routed and inspected for attacks. The pros include a simple/single component that needs to be deployed and managed away from the application hosts. Also, it is hardened or monitored in a way that might be burdensome across all hosts. An individual/shared view of security exists in a single place so that the big picture can be inspected for anomalies/attacks.
However, a network-based IDS includes the performance hit of adding a network hop to applications. The need to decrypt/re-encrypt traffic to inspect it is both a massive performance hit and a security risk that makes the network appliance an attractive target. Any traffic that IDS unable to decrypt cannot inspect/detect anything.
An IDS is a detection and monitoring tool and does not act on its own. An IPS detects, accepts, and denies traffic based on set rules. IDS/IPS solutions help to prevent DDoS attacks due to their anomaly...