What is the main purpose of using Access Control Lists?

Access Control Lists (ACLs) serve the essential function of defining how network packets are handled as they traverse through a network device. By employing ACLs, network administrators can specify the criteria that packets must meet to either allow or deny passage. This ability enables fine-tuned control over traffic flow, enhancing security by permitting only authorized communications and blocking potentially harmful or undesired traffic.

In the context of network management, ACLs help maintain the integrity and security of the network by controlling access to resources and services. By determining which users or devices can interact with various protocols, hosts, or services, ACLs contribute significantly to the overall security strategy of a network.

Other options like monitoring network speeds, logging network issues, or increasing performance are not the primary functions of ACLs, though they may be secondary benefits derived from effective network management and security practices. Thus, the emphasis on packet handling clearly substantiates the answer as the correct choice.