Why is oleophobic coating necessary for tempered glass screen protector?

We all know that tempered glass screen protector is anti-fingerprint, waterproof, that is because of the oleophobic coating on the glass.

After tempering process, the glass will be cleaned by ultrasonic cleaning machine, then spray oleophobic coating on it. Usually there are two ways to coat, manual spraying and automatic spraying by machine. After spraying, the glass will be dried in industrial electric oven. The whole process is completed in a dust-free room.