I started back pocketing a couple months ago. I just got sick of all my jeans developing a perfect outline of my iPhone faded in the front pocket. I have no idea why it happens, but it's definitely not a good look having a rectangle on the front of your pants that shouts "HEY EVERYBODY THIS IS WHERE MY PHONE GOES"
And unless you're wearing JNCOs or some really baggy jeans, if you have the 6 plus in any pocket, it's going to look like you're walking around with a paperback in your pants.