We recently launched our intranet and someone already changed the left side navigation. What level of permission is required to use that? I can't find that in the permissions table. Most authenticated users should only have read access and none of the admins will admit to making the change. BTW, I know I could hide it with CSS but the admins should be able to edit these links and wouldn't be able to if they were hidden by rule.
I suppose better than hiding the controls, creating groups with different permission levels like Read, Contribute, Full Control etc. might be more useful for you. You can have a look at the different permission levels here