When I fly my Phantom 4 with Ipad am I then supposed to switch off the wifi and put the dial to fly mode on my Ipad?

You shouldn't have to, but it wouldn't do any harm if you want to set iPad to 'airplane mode'.

You would likely see no difference either way.

I think airplane mode is a good idea especially if you fly near your house, because otherwise you will get pop ups saying YOU HAVE MAIL and other such nonsense, and you don't need the distraction.  

Good luck

Hi there, thank you for reaching out. Captain @Aardvark and Captain Mark The Droner is correct about this. I agree that you can turn it off to avoid any notification that will lead to interruption or distraction. Best regards!