You know, if people could do this there would have to be people to regulate it and keep people from going on rampages; because these things are pretty much alternate universe hatcherys and all those people you kill really would be killed even after loading your previous save.
There would need to be some sort of Save Police or whatever and lots of people doing this constantly would probably break the universe or create so many splinter universes that reality wouldn't exist anymore and it would all be really forgeted up with almost no way of correlating between these universes because each one is different.
This is making my head hurt and now I'm making run-on sentances damnitforget.