Top reasons why you should choose iPhone 7 Plus over iPhone 7 from a professional photographer's point of view
Bigger screen: lots of room for everything especially now that you can shoot and edit RAW directly from third party apps like Lightroom.
Dual camera system: double the pleasure / if you ever used digital zoom, you can stop using it now. Dual lens system allows you to switch lenses easily to go from wide angle to telephoto
Most DSLRs and mirrorless cameras now come already equipped with WiFi now so bigger screen means bigger viewfinder. Connect your iPhone to your camera and voilà, you're now equipped with a portable gigantic viewfinder ready to shoot from the most interesting angles.
Longer battery life to extend that Insta photo sesh!
I've been using a 5.5 inch iPhone for two years and I wouldn't go back to a smaller iPhone: I got the iPhone 6 and iPhone 6S as soon as it got out and never regretted my choice. I just love the horizontal view in many apps like Mail for instance. It really allows me to be productive while not carrying a heavy laptop around (my photo bags are already heavy enough!)
Perfect for watching your favourite videos on Netflix or iTunes Store. The size of the screen is so awesome I don't even carry an iPad for watching Netflix anymore
Best viewfinder for your drone: you have already SO MUCH to carry around when you own a drone. Save some space and weight by using your iPhone 7 Plus as your viewfinder when controlling your favourite drone (like the DJI Phantom 4)