So if you use primarily a doubler or other setting , you can lock that in along with the harmony to lead ratio..then go back and customize for other harmony parts to specific songs while maintaining ratio. I imagine unlocking/relocking would be required or a similar save function. Idea is to set most but not all to same setting without saving 300 times in songbook or registrations/presets.
Last Korg I had was a pa600 but even that had many global settings as opposed to Yamahas I had later. I think that makes it easier to get started enjoying the board followed by song specific customization.