It would mean it's a lot harder to get viruses. If only apps checked by microsoft can be installed from their store, it is more secure. I think secure would be a better description than safe. That's why you can't go back, because Microsoft can't guarantee what you have done to it while it's not in S mode. For people in your wifes situation, if she can get everything she wants from the store, it is not a bad idea. Naive computer users are the ones most vulnerable to hacking.