Most modern smartphones use scratch-resistant glass on their screens, but every once in awhile you'll see that your phone still gets some fine scratches. XDA Developers nails down the source: it's not the change or the keys in your pocket, it's the sand.
XDA does a bit of experimentation with a number of Spigen screen protectors, which use tempered glass to keep scratches off your phone (not unlike the "Gorilla Glass" that coats most modern smartphones). They test it against keys, coins, sand, and other materials to see what scratches it the most. Surprisingly, most materials didn't leave a mark, but that hard, gritty sand that's floating around in your pocket—or on your desk, or anywhere else—actually has the potential to leave some scratches in your phone, showing us that screen protectors can still be useful. Check out the video above to see their tests in action (though close your eyes at the end, it gets pretty scary when she does the drop tests).
I didn't have a screen protector, but if I have to pick a reason, that because I want to avoid scratch (before I see this thread).
However, it seems since iPhone 6, the glass are more scratch resist. I use my 6+ since day 1, and still no scratch without any screen protector. Of course I will try to avoid the risk (e.g. won't put it in the same pocket with my key), but apart from the obvious precaution. I didn't baby it too much, and just use it normally.
TBH, fingerprint is quite annoying, if a screen protector can avoid that effectively, I may get one for just this reason (after seeing this thread).
Back tempered glass is up to you, and yes the phone can definitely get scratches even in a case. Most case manufacturers even recommend removing the phone from the case periodically to clean it.Do i need to add back tempered glass on the rear of iPhone?
If i put my phone under case, does aluminium get scratch overtime when dirty/dust will inevitably making contact between case and rear of phone?