Many people think that seat belts in cars are important only if you get in an accident to prevent the driver or passenger from being thrown around inside the car or ejected out of the car. While that is true there is an important prior reason to wear seat belts at all times.
People do not realize it but when they don't wear seat belts they unconsciously have to brace themselves to maintain their seat behind the wheel. If you have a sudden event, where you have to brake or navigate drastically, the seat belt prepares you to be successful in that event because no part of your body is trying to brace itself behind the wheel. This is why a driver who does not wear a seatbelt is more likely to lose control of a car in a sudden event than one who is wearing a seatbelt (assuming all else is equal, such as the skill of the driver). An example of this is when airplane passengers are told to put on their seat belts when air turbulence is encountered so they don't jounce around. It's the jouncing around I am talking about. When you are relaxed and tooling along in a car there's no problem, but when you suddenly have to react, if you are not strapped in you are either jouncing or having to fight the jounce that comes with a sudden change in your position while having to brake or steer. This all got clearly explained when I was in drivers education back in the 1960's. People don't seem to mention that aspect of it too much nowadays when they debate whether drivers/passengers are at fault for disobeying the law and not wearing their seatbelts. The point is not just to worry about injury from being thrown about in an accident, the point is that by being held securely to your seat you can be quicker and more accurate in your physical reflexes than if you are fighting to keep your position in the seat or actually losing the ability to reach a control because you are trying to brace yourself. Any race car driver can tell you the same thing that having a firm and secured seat position empowers you to respond more strongly and accurately with your movements to control the car.
In fact, here's a little social history. I find that as I've gotten older it helps younger people to hear some of how it really was in order to understand what I'm saying. There was a big debate about whether to use seatbelts in the 1950's and 1960's and you might think it was odd but it was regular family men who were against wearing them. This is because these guys grew up learning to drive one of three ways: driving a tractor on a farm, driving a jeep in the army, or driving in very rural country roads. They worried about being able to "jump out in a hurry" if they were in an accident. This was because if a tractor or jeep overturned, you were trained to jump so you would not get caught or crushed under it. So our dad's generation (your grandfather's generation and great grandfathers) learned to drive in a less congested and combative traffic environment and more as a farm or military context of driving. It was exactly what I said above that finally convinced enough of them to put seatbelts in cars in the first place and start to use them. When that dad generation started understanding that it was more like being an airplane pilot than a tractor or jeep driver, where jumping out is no longer as important as maintaining control over the car, they started to come around and understand why seat belts were needed and actually helpful rather than a hindrance. I listened to those debates many times as a kid, lol. But that was when the roads were still country roads by definition (before highways for the most part) and nowhere near as urbanized, busy, and fast paced requiring fast reflexes as they are today. Hope this helps!