Example use case: I want to pre-populate the canvas with background content (images, diagrams) that the team can draw over/inside but shouldn't be able to move or edit.

In groups with trust, it's okay if the ability to "unlock" is still shared by all editors -- for me, this is less about safety/access control and more about bringing down the number/real-estate of editable objects in a complex canvas, which reduces the impact of mis-clicks and makes selecting important objects easier.