I choose not to use 2factor because every extra step is a PITA. To compensate for my astonishing lack of security awareness I don't take nudie pics.
It only seems to come into play when you want to access your iCloud/iTunes account from a new device. I just bought music from iTunes on the computer I set up two factor on and it didn't come up. It came up when I rented a movie with my AppleTV but it wasn't a big deal to type in the four digit number Apple sent to my phone. Probably won't come up again for that device, either. Not really a PITA in my opinion, except for the person trying to break in, so I think a little extra effort is worth a little more peace of mind.