What are the '~previous', '-previous' and '~orig' files in /private/etc/?
The ~orig and similarly suffixed files are previous and likely corrupted versions of the settings/plist file where the "current" one is pretty much a duplicate of the "bad"one, not helping most situations (like when your ~/Library/Preferences/com.apple.iTunes.plist is corrupted). 

In my experience though it usually ends up that the current file still has part or most of the corruption the previous one had. Depending on the location, it should be safe to delete the ~orig and similarly named files. 

The current ones in /Library/Preferences should be safe to delete, I've never had negative results from that. 

In the previous iTunes example, the freshest plist still may cause wonkiness like slow start and quit of iTunes. I had this happen to me about ten years ago, took 5 minutes to open iTunes, 10 to quit when I had this issue. When I checked the plists I must have had 200+ bad copied (in this case they would be com.apple.iTunes.plist. ). Removed them all and reopened iTunes, it created a new plist without trying to inherit any issues from the previous ones and it was smooth sailing since. 

But like I said earlier, the ones in non-user and non-/Library/Preferences I would leave alone or be careful with, especially in /etc and /private.