Rebooting and turning it off and back on are slightly different. And my observation is that turning it off and back on after an iOS update is needed more often than not.
Many devices go thorough a reset/test sequence when powered on that they don't necessarily go through when it is rebooted. Also ram gets scrambled when the device is powered off.
As I've said elsewhere, I had battery life issues on a couple of iOS devices after an upgrade until I turned them off and back on. I have no solid data to back it. But it's what I've observed. And for all that it takes less than a minute, it can't hurt.