Replication lag is a critical indicator of replica set health, but it's not the only factor to consider. The size of the oplog and the volume of operations also impact infrastructure health. The replication oplog window, which measures the time difference between the oldest and newest entries in the oplog, has two significant consequences: it determines how long a secondary member can be offline before catching up with the primary without doing a full resync, and it sets the maximum amount of time for the initial phase of a full sync. Understanding these factors is crucial to maintaining healthy replica sets, as fluctuating replication oplog windows can indicate peak traffic periods that require capacity planning adjustments.