Dan Frakes discussing why he might be getting an iPhone 6 Plus:

It wasn’t until I stopped thinking of my iPhone as a phone, and started thinking of it as a computing device, that I warmed to the idea of a honking-big smartphone. My hope with the iPhone 6 Plus is that I’ll find myself carrying a second device much less frequently. Sure, the 6 Plus may be bigger than the “perfect” phone size, and it may be a tight fit in my front jeans pocket, but it’s still incredibly small for a powerful computing device, and as long as it fits in my pocket at all, it’s better than carrying a smaller phone and a bag or sleeve with an iPad or laptop inside.

A 5.5” device used as a phone is just too big and makes anyone look ridiculous. I’m trying to think how often I use the iPhone on to my ear, and the conclusion is that it’s very rare. But then I think that a 5.5” device in my front pocket would be too bulky.  

A 4.7” screen seems a good compromise, but with a 5.5” I could get rid of an additional device to carry around, the iPad.