When do you reboot an ESX host? When there's a problem with it. Obviously if the hosts and guests are running fine then you wouldn't need or want to reboot the host. This may sound trite but there really isn't a good answer. When do you reboot a piece of equipment? When it needs to be rebooted, which should be fairly evident.
My apologies for the misunderstanding. My answer didn't state that you should reboot it regularly. My answer stated that you should reboot it when there's a problem. How else would you know when to reboot it? If things are running fine, would you reboot it? When things are not running fine is it apparent to you that they're not? In your first comment to my answer you said that you couldn't wait around to recognize a problem and you need to be proactive so I said to regularly reboot it then. You can't have it both ways. You either wait for the signs of a problem or you reboot it regularly.
Q: "How do I know when to reboot it?"
A: "When things aren't running properly."
Q: "But I can't wait around for a problem, I have to be proactive".
A: "Then reboot it on a regular schedule".
I don't see any other way of looking at this.