With snap turns, you can use a button on the controller to turn in VR by a set angle. Usually the button is the joystick or trackpad. Some apps use a swipe motion, while others use a tap.
Pros: Makes it much easier to use VR apps without having to physically turn around or swivel your chair. Causes less motion sickness for some people than manual turning.
Cons: - People who don't get motion sickness and use VR a lot prefer to be able to turn manually, rather than having the turn angle chosen for them.