It shouldn't be needed, however sometimes if the phone is behaving weird after the update that can be caused by something left over from the previous version and a reset could fix it - but again, should be the last resort. Sometimes people also say that you shouldn't transfer all settings with Smart Sync between an old and new device, as that can mess up the new one. I have never experienced that myself, so I would say don't bother with clean slates or resets unless something is behaving weird or not working. 
