This OID counts leases that expired naturally when the client did not renew before the lease duration ended, freeing the address back to the pool. Monitoring expires helps administrators understand whether lease duration settings are appropriate for their client population. For instance, if expires equals 340 in a week while lease duration is set to 8 hours, it suggests many devices are shutting down gracefully without sending RELEASE packets, which is normal for office PCs that power down each night.