Point of profile manager if user can change it anyway?

I'm not sure I understand the concept of profile manager. What is the point of the profile manager if the user can change anything?

Say, I set some login items for all the users in the office. The user can just go into preferences and just remove it!

Say, I set some policy on the dock. The user can just go into preferenes and change it....

Can someone explain? Maybe this is more designed for the iOS?