As I work with clients and on my own projects, I'm finding it's hard to get a quick, concise view of what they're seeing. As a Project or Account admin, I have to click into each individual folder of a project to review permissions.
I recommend a "preview" mode that lets Admins flip to a project account/ Role/ Company and see projects as that Viewer. This gives Administrators a VERY handy tool to quickly see what their users are seeing and troubleshoot permissions and problems in workflows much more effectively.
Such a mode would be a preview-only, you wouldn't be able to add issues/ markups/ comments. I envision it would have a toggle similar to the "Preview Visibility" function in Revit's family editor.