With the Network Proximity Checker, a game running on a client doesn’t have information about game objects that are not visible. This has two main benefits: it reduces the amount of data sent across the network, and it makes your game more secure against hacking.
This component relies on physics to calculate visibility, so observer game objects must also have a collider component on it.
A game object with a Network Proximity Checker component must also have a Network Identity component. When you create a Network Proximity Checker component on a game object, Mirror also creates a Network Identity component on that game object if it does not already have one.
Scene objects with a Network Proximity Checker component are disabled when they're out of range, and spawned objects are destroyed when they're out of range.