I don't know if it's where I live (near the beach) or fairly active life style but I always am prone to micro scratches.
I am very careful with my phone but I do use it a lot when I'm out. Therefore I assume micro specks of dirt or sand might land on the screen and if I happen to swipe in that spot a micro scratch occurs.
These scratches are actually really hard to see. If you tilt your screen just right in just the right light you can see a very faint scratch.
For this reason I started using glass screen protectors on my 5 and 5s and now my 6. I could careless about the micro scratches on the protector because that can easily and cheaply be replaced.
Another reason to use glass screen protectors is the oleophobic coating. The stock coating for me wears away after about a year. With a glass screen protector when it wears away you can just replace the screen protector.
what screen protector do you use ?