Auto unmount in Big Sur

Can someone who knows explain the usefullness of the auto unmount of system volumes feature that I have seen in Big Sur beta 1 +2? And How can you unmount root? Cached?
It even unmounts my mojave and catalina boot partitions.
I have noticed this in disk utility. A bug?
It seems this behavior is gone in beta 3 of Big Sur for the other macOS partitions. Now it only unmounts root. Start up
disk utility to see this. Disk utility can now mount the system R/O volume unlike in beta 1 + 2
Auto unmount in Big Sur
 
 
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