A. Full-face hard helmets have several benefits. They help protect the face from the feet, elbows and knees that skydivers occasionally encounter on exit or in freefall. They're warmer than a leather hat, and shield one's face from rain. Hard hats almost certainly provide some impact protection from a hard landing, although helmets don't meet any safety standards, nor do their manufacturers claim any sort of protection. They're also easier than goggles and a hat to slip on right before exit.
Some people think they look cool.
Those are the benefits of hard hats. That's double the price of many goggles, but jumpers report they last longer than goggles. Many of the designs need work. Different models and brands fit different people differently. Like shoes, you need to try a hat before buying it.