Case Merge is a native feature that allows agents to merge up to three duplicate cases into one master case, and delete the other cases. Case Merge preserves the case history, comments, attachments, and related records of all the merged cases. Case Merge can be enabled from Setup > Case Merge Settings. Verified References: :
Merge Duplicate Cases in Lightning Experience

Case assignment rules are rules that automatically assign cases to users or queues based on certain criteria.
You can create a case assignment rule to ensure that cases are owned by a user when they are closed, by setting the criteria to match the closed case status and the action to assign the case to the user who last modified it. This way, you can prevent cases from being closed while still owned by a queue. To correct the existing problem of hundreds of cases that are closed but still owned by a queue, you can use a data tool such as Data Loader or Import Wizard to update the owner field on those cases in bulk. Verified References: [Case Assignment Rules] and [Data Tools]

Agent utilization is a key metric for assessing the effectiveness of workforce management systems, as it measures the percentage of time agents spend handling customer interactions compared to their available time. Improvements in agent utilization indicate a more efficient allocation of resources and better capacity planning.