Currently, "Viewer" and "Checker" Permission Levels provide Zero Security. Instead, they actually provide Viewers and Checkers with the Option to Copy a Project over to their very own private Workspace and assume ownership of what was supposed to be a "Viewer" or "Checker" only Project. Once owned, they can do anything they want with the Project.
Within the "Viewer" or "Checker" Roles themselves, users can also:
1) Print
2) Export
3) Add to Templates
All of these abilities are far beyond what a "Viewer" or "Checker" should be able to do!
While anyone can ultimately Click & Drag down a Project's page to copy and paste it elsewhere (unless this too could be prevented), it would still be better not to enable or even give Viewers & Checkers the very idea of copying, etc. which is currently being actively promoted by providing them with readily available options to violate their Given Permissions using the App itself.