When you don't need to keep read posts, you delete them. However when you monitor too much feed, managing that much load and deleting those unnecessary posts can be hard to maintain.
To ease the maintenance, Newzie provides two useful tools. One of them is Trashbin and the other one is the automated maintenance of the sytem.
While Trashbin keeps deleted posts in the system for a while, automated maintenance runs a post sweeper that you set in the system periodically and remove those unnecessary posts at each run.
Maintenance-related settings are set thru the tab named 'Maintenance' in the Preferences dialog. Following help topics show you how to customize these two tools based on your needs.