system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Most 3D renders (like Blender) can render via GPU or CPU? Why not both at the same time for maximum efficiency?
gpt
It takes a lot longer to send information from the CPU to the GPU and back than you would think. Processors are fast, but transfer speeds between parts on your computer slow compared to that, so it would take longer to have both the CPU and GPU working on it at the same time than it would for just one of them to do it.

Imagine trying to draw a picture with someone else. That someone else is several miles away, and you have to send it in the mail every time you want the other person to make changes. Sure you have twice the man power, but it spend so much time in transit that it would take a lot longer to get done.