How to stop blender from rendering world I have an animation where some cubes are floating around on a pitch black world:



Since these are jpegs, you can't see that I chose blender to render the world transparent. But when I render, Blender will waste time rendering the transparent tiles. Even though it's only for a split second, it adds up to alot of time since it's an animation:

 

How can I stop this?
Short answer: you can't.

Cycles can't skip parts of a render based on what is/isn't there because it doesn't know what will be there until it has already rendered it.  So it can't skip tracing rays that only hit the world background since it doesn't know what a ray will hit without actually tracing it.