Is a screen protector useful on a Gorilla Glass phone? I bought a 2nd generation Moto E phone. According to this page at GSMArena.com, this phone has a "Corning Gorilla Glass 3, oleophobic coating" screen.

I have seen many on-line shops selling "tempered glass screen protectors", a layer of plastic one can buy to put over the screen. I found this useful with some older devices I had, where the screen could easily become dirty and scratched. I am mostly concerned about being able to easily clean away fingerprints and to avoid having scratches caused by fingernails or creating worn out areas of the screen, due to frequent use.

Is such a screen protector at all useful on a Gorilla Glass screen?
No matter how hard glass can be, it still is limited to the Mohs hardness of the material (&lt;7). In day-to-day use, it has to face the occasional harder matters it encounters, such as Quartz (7), SiC (9.5) or even Diamond (10) grains hidden in sand.

As for the oleophobic coating, while the quality of the original coating is superior to those on the 3rd-party tempered glass films (not to mention plastic films which has no such coating), it still will gradually wear out especially under repeated friction of fingers and organic solvents such as Alcohol, and once it does there's no going back unless you replace the screen itself.

Applying a film, in both cases, is a sort of degrade in experience: you lose the general smoothness and gain a bit more scratches on the film itself, but in exchange, once the scratches or wear of the coating accumulate to a certain level, you could just replace the film at a very low cost, and the experience will be close if not equal to new.