Hardness

Also, powder coat is physically harder than wet paint, which makes it more scratch and chip resistant with a higher durability rate.

Adhesion

Powder coat also has a higher adhesion rate than spray paint, partially due to the significant pretreatment.  Increased adhesion also means increased resistance to chipping and corrosion

Dry Film Thickness 
Powder coat is applied at a thickness of 2-10 mil, determined by the need. (Functional finishes are usually thicker than decorative finishes.) This is 4 to 10 times thicker than the 0.5-1 mil traditional application of liquid spray paint. 

Corrosion Resistance

Properly applied powder coat far exceeds traditional spray paint's ability to prevent corrosion.  Test results show that the lower application thickness for decorative use powder coated items do not show signs of corrosion even after going through salt spray tests for more than 1000 hours - and, thicker functional coatings are even more corrosion resistant. 

Flexibility
Powder coat is actually a flexible products, with published test results showing 100-800% elongations before failing! This flexibility also contributes to the resistance to cracking or flaking when the part is manipulated.

Environmental Impact
It's common knowledge that wet paint is flammable, but many people don't know it's also carcinogenic (can cause cancer), and contains Volatile Organic Compounds (VOCs). On the contrary, powder coat is environmentally friendly, as the powder is not a significant health, fire, or environmental hazard. Additionally, the powder is applied when it's dry using an electrostatic bonding process that that allows ~90% of the powder to adhere to the item - and, the remainder falls to the ground to be collected and disposed of instead of going into the atmosphere. Thus, powder coating has a minimal amount of waste. Spray painting efficiency, however, is often below 50% and the paint that doesn't adhere goes into the air or settles onto nearby objects, unable to be reused.