Not the OP, but I think they mean that the change to the rules is done to reduce the search tree a program should traverse but makes it difficult for a human to

Not the OP, but I think they mean that the change to the rules is done to reduce the search tree a program should traverse but makes it difficult for a human to reason about. We search for solutions heuristically and because of the added rules must back track a lot more, which makes it tiring. So, the change makes it easier for a computer but not for a human.