The original script of The Matrix had the Machines using human brains to perform computations - both out of a sense of vengeful justice, and because it was convenient to use human neural nets for certain kinds of tasks.

There may even have been a suggestion that the physics of the world permitted humans to do things that the Machines couldn't - something along the lines of the AIs being implemented in digital hardware instead of analog.

This was changed in the script because it was feared most viewers would not be able to understand the idea. "Humans as energy resource" was substituted for "humans as processing resource".