How the Digitizer / Touch Screen Works
There are two layers of glass for the digitizer assembly. The first is simply glass, which is what you touch. The second is attached to the glass and senses the touch via an electrical field which transmits and receives based on the "return" from your finger or stylus. The digitizer and LCD work independently from one another. So if one fails, it won’t necessarily cause the other part to fail. With cracked glass, you can see the content on your screen, but there is broken glass which makes it hard to see. Cracks, splinters, and shattered glass can be present while the digitizer is still responsive. However, the digitizer can fail over time.
Preventive measures include using a case for your phone that creates separation between objects and the screen. Cases that don´t create a ridge on the glass side of the screen may be fashionable, but they don't protect the glass. And screen protectors will only prevent scratches.
Digitizer (Touchscreen) Failure is when a phone stops responding to touchscreen commands. This can occur with impact damage (usually associated with cracks in the glass), extreme heat (such as lying in the sun for extended periods of time) or water damage to the device.
Remember that glass can scratch from a variety of things, including keys and rough surfaces such as concrete or pavement. Glass can be replaced to make your cell phone look new again. But try not to drop your phone!
Use a screen protector to prevent any kind of damages, but remember a hard case is always better. It's always cheaper to buy a case than having to replace or repair your device.