running a program sandboxed vs running a sandboxed program

[wormbucket]

What is the difference between running a program, which was originally installed outside the sandbox, as sandboxed, and running a program which was originally installed in a sandbox? Advantages or disadvantages?

Would there be any conflicts if I had a program installed outside the sandbox, and then installed a different version of that same program inside a sandbox? Would I need to first uninstall the program outside the sandbox?