I wonder if objects outside camera frustum are automatically culled? If so, does it make sense to place a Cull Distance Volume in a pure top-down view game?
Probably it’s a silly question, but it keeps bothering me 
I have this same question too, sadly nobody answer in 6 years 
The answer to the overwhelming majority of performance questions, including this one, is “try it and see”
My wild guess is that in most cases it’s not worth the effort. But I could also construct a scenario where it would be very useful. For example allowing the camera to zoom really far out. Or letting the player climb to a high point and traverse a narrow bridge, such that most of the level below is still in view.
A “top down camera” doesn’t necessarily mean everything in view is going to be a fixed distance, which is why it is important to test these things on your particular scene.
I wonder if objects outside camera frustum are automatically culled? They are, you can test this with the FREEZERENDERING command that will freeze the render engine and you can move around to see what’s getting culled. Sometimes, objects that we think should be culled, won’t be because the camera sees 1 pixel from it and so it leaves it in the scene, that’s where cull volumes come in.
I have a world with a traffic cars, and they are really expensive. Even if they are outside the camera the FPS is going down, cpu used to calculate I suppose. S I was thinking if culling they will “stop”.