How and when to perform housekeeping on the system
Locked checkpoints are useful to be able to revert a standalone node or a primary node at a specific state in the past. But old checkpoints prevent a node from deleting data files that were useful when the checkpoint was created but that are no longer relevant. Checkpoints that are not locked are automatically purged after a while. Locked checkpoints, however, are kept until they are unlocked.
As a consequence, you should keep the number of locked checkpoints as low as possible. You should also avoid keeping a checkpoint locked for too long.
To delete a locked checkpoint, simply unlock it. The node will delete it shortly after. Read Unlock a checkpoint for the procedure to unlock a checkpoint.