We have seen the Kyuubi is both malevolent and capable and willing take over, so it's well within the realm of possibilities it would help with Naruto's mental exhaustion by relieving him of the stress of being in control. After all, Naruto's mental exhaustion isn't the Kyuubi's mental exhaustion. Our demon fox would be as sharp as ever and Naruto could relax by sleeping in the background.Originally Posted by Abdula