Activating locking
What does activation do?
Activating locking enables the Locking SP, which makes the locking and encryption features of the device available. This is also a single step process, and you will need the owner's password you have just set, as well as provide a new password for the administrator authority that will manage locking and encryption features from now on.
The Admin1 password
SEDManager gives you the option to reuse your owner's password as the locking admin password. You can use this option for simplicity in case you're the only user of the drive or you will be the only one managing the device's configuration. There is very little safety concern in reusing the password, and you can change both password independently afterwards.
Enabling locking will not erase your data, but later disabling it will. While you can just leave locking on, it's not recommended unless you are using it, so make sure you really want to enable locking or prepare to back your data up when you disable it.