BitmapText#autoCull

A Game Object with autoCull set to true will check its bounds against the World Camera every frame.
If it is not intersecting the Camera bounds at any point then it has its renderable property set to false.
This keeps the Game Object alive and still processing updates, but forces it to skip the render step entirely.

This is a relatively expensive operation, especially if enabled on hundreds of Game Objects. So enable it only if you know it's required,
or you have tested performance and find it acceptable.