What exactly does the ‘Save for all users’ option within ‘save as’ do?
Does it open up the universe for users to create reports off it?
Does it open up the universe for users to modify the universe?
In Best Practice terms when should this option be used?
Crash 
(BOB member since 2004-04-27)
You need to use Save for All Users when you want to distribute reports or universes from a repository to someone who isn’t part of that repository.
When you try to open a report or universe, BO will try to check against the repository to see if you have rights to do so. If it can’t find anything to say that you are permitted to, then you get a warning about not having the rights to open/use the report/universe and it will not open/appear.
The exception to this is when a General Supervisor account tries to open/use the report/universe. They always have access to everything, and will be able to use the files.
Generally, you only need to use this option when transferring reports or universes between repositories or when sending them to a user who doesn’t use a repository.
Paul Williams 
(BOB member since 2002-07-10)
Paul is 100% correct … behind the scene’s, what’s happening is that the security bit gets removed from the report so that it looks like it’s never been exported to the repository
Chris Pohl (BOB member since 2002-06-18)
And I am sure that Reporter Bloke will be able to open the file in a hex editor and find some switch that will turn on save for all users. 
Randy Jones (BOB member since 2002-08-19)