If context rules are in use for your navigation windows there may be processes that are prepared for some users which you as a PM and Modify user cannot normally see, for example a light manage stages process just for a team member.  Without access to it you could not customise it so a Admin user can always use the View Process Images form which overrides the context rules and allows any image to be viewed.

The form gives a list of all process windows these can then be opened and the required process selected.

Note: context rules control access to the navigation diagrams not to the processes themselves.