Higher standby allows you to pick it up and go without worrying about needing to charge while out and about. That said, do you experience any battery difference between power off and boot the following day?
My suggestion applies best to cases where you are settling in for a bit of time and when finished won't be using it for a significant period of time.
Not sure I understand your question about battery difference. Battery capacity is pretty much exactly the same as when I turned it off, but frankly haven't paid that much attention to it.