Current law in California is that employers can still fire employees for simply having smoked pot regardless of whether the employee was prescribed the marijuana and there is no need to show that the smoking impacted job performance. This was confirmed by the state supreme court in
Ross v. RagingWire Telecommunications in 2008. So in that regard this initiative would appear to overturn that. I'm sure that the FAA will still be able to pull you pilot's license or that Berkeley will be able to deny you a job at Lawrence Livermore if pot smoking is against the rules.