You data is encrypted on the device... so now let us decryp everything on the phone, or virtual machine or otherwise....

Point being: option per device to allow or NOT of what to even be loaded. It's not even "to be access" but "it never even shows".

This is very usefull if we want want max control, and max privacy. As in for phone? we can have our proton drive open, unlocked, and if we show someone some pictures from there, they simple can't access, not even realise, that other parts even exist.

This also means if we use our phone, virtual machine, or similar, we can ensure that, even if someone else is accessing our data, there is nothing, aka not "it's hidden but there" or passwords, no it "never" existed on this device. Meaning that yes, it is hidden and password protected, but it's not the folder/file, but for it to exist on the device or to see in not on the device but on the cloud storage.