Glass coatings are hydrophobic coatings that increases the surface contact angle of water with your car's paint. This is better known as the "lotus leaf" effect. The water droplets that come into contact with the glass coating surface rolls off easily, carrying with it the dirt and dust from the paint surface. Apart from that, a proper glass coating provides adequate protection for the physical gloss levels of the paint surface. Actings as a barrier of defense for the original paintwork against minor scratches and swirls.
Here is a video showing excellent hydrophobic effects after a full year of a usage.