Can a ceramic coating protect a car from scratches?
Quick answer: Ceramic coatings don’t make cars scratch-proof, but they can reduce wash marks and lessen damage from many everyday contact scratches by toughening the paint surface.
A ceramic coating does reduce scratches, and the difference is noticeable. It will not make your car scratch-proof.
Ceramic and graphene coatings are the toughest finishes available, with a 9H rating, so they are about as scratch-resistant as a paintwork coating gets. If someone keys the car or drags a bike along it, a coating will not save you. Lighter marks -- the kind you pick up from a bush next to the drive -- are often reduced significantly. Trim the hedge anyway.
You can still pick up scratches, but they tend to be shallower and less likely to cut through the clear coat, which means a professional can usually polish them out.
Self-cleaning behaviour also plays a part. Dirt releases more easily and the car needs washing less often, which cuts down on micro-marring and wash marks from grit trapped in a wash mitt.
Worth knowing: not all scratches are equal. When people say "scratches" they usually mean one of three things -- fine wash marks, medium contact scratches (hedges, dog claws, bags dragged across the boot lid), or deep impact and vandal damage. Coatings help with the first two more than most people realise. When the paint surface is harder than the object that hits it (a plastic wing mirror, a cardboard box, a dog's claws), you are more likely to see paint transfer onto your car than a gouge into it. The mark looks like a scratch but often polishes out because the damage never reached the clear coat.
For vehicles that will definitely see impacts, we suggest Paint Protection Film on the vulnerable panels. It offers far greater protection as a sacrificial layer.
For the broader "why have ceramic paint protection" answer, see What are the benefits of a ceramic coating?.