What triggers BitLocker to lock?

Could you please elaborate on the specific conditions or events that prompt BitLocker to activate its encryption and lock down a device's drive? Are there any common scenarios or user actions that typically initiate this process? Additionally, is there a way for users to manually trigger BitLocker to lock their drives, or is it solely an automated response to certain triggers? Understanding these details would be invaluable in ensuring the security of sensitive data stored on encrypted drives.