"Unknown Sources" checkbox switches from a user setting to a permission on Android Oreo7
The change in Android Oreo is important because it makes it safer to install apps from unknown sources. It prevents another app from asking you to install a bogus software update that contains malware. On Android Oreo, you cannot be fooled into installing the bogus software update without granting permission first to the app that prompts the install. You might consider this to be a pain in the butt, but considering what could happen without this change, you really should be willing to take the time to give permission before installing apps from unknown sources.
Check out our Android 8.0 review, hot off the press, by clicking on this link!