That protects you from bacteria that are likely to be on your hands from encountering your eyes, mouth or nose, and gaining access to your system. Thirty percent of Americans still don't do that. Those thirty percent and everyone else should not only buckle-up, but should do it right. Studies have demonstrated that many who buckle-up don't do it right. Look in your car's owner's manual for advice on the subject and the warnings, which are many and important.
Most people find the seat belt information in their owner's manual a revelation.
If these rules are violated serious injury or death may result. There are many other warnings and directions that any user should be aware of. I'd add a few more to the list, realizing dozens and dozens of other lifesavers could easily be added. I'd add read the owner's manuals of the products you buy, including your car, car seats, smoke detectors, and all the rest. By doing so, you assure you'll use them correctly to gain their benefits, and you may avoid their misuse which may result in disaster.