Most cameras, especially professional and enthusiast models, come supplied with a neck strap. Using a neck strap does have many benefits.
The benefit of using a shoulder strap like this is that while walking, the camera will not bounce around on your chest like it often will when using a neck strap. It also puts the camera by your hand, making it quick and easy to bring up to your eye. If you also own a camera, then you must navigate to https://gariz.com.au/collections/shoulder-straps to buy a camera shoulder strap.
Having the camera hanging by your side is also slightly less conspicuous than having it hanging around your front.
Frees your hands
The main benefit of using a strap is that you don't have to keep hold of the camera with your hands. You can use both of your hands for other things, while the camera hangs safely from the strap.
For users of interchangeable lens cameras, this means that you can easily change lenses on your camera without having to put the camera down anywhere. When you're in a situation where you don't want to put the camera e.g. in a muddy field, this is very handy. Even in situations where you can put the camera down, not having to do so can make lens changes much quicker.
Secures your camera
A strap can act as a fail-safe. If you drop your camera, the strap will save it from falling to the floor. You may think that you would always keep a good grip on your camera, but in busy areas such as markets or people rushing to catch a train, you could take an unexpected knock and lose your grip. A strap helps in these situations.
Similarly, a strap makes it much harder for a thief to steal your camera. They can't just grab it out of your hands.