but can't think of a possible use for this switch.
As a 'security' feature, it's useless, anyone could switch it on.
As a 'data-protection' feature, it's useless, because it doesn't let you see the drive at all, let alone see as read-only the files on it.
In effect, it achieves pretty much the same thing as removing/disconnecting the drive....
... any ideas how it could be usefull ?