The battery and dual lens camera are both killer reasons to go plus! Also you get used to the size super quickly, which I had never expected, but these two plus the bigger screen make this the best iPhone I had since the 4!
All of the plus' benefits were major factors. Larger screen, higher resolution, better battery life, dual cameras. All things I wanted. I was also left wanting a bit more after I got my regular 6. The only negative I have about the plus is the pocketability.
February 2015: I got the 6+, 128GB because it was the largest iPhone model I could gouge Sprint for both in size and capacity and price. At that point I was very angry that Sprint still could not provide decent LTE coverage and speed in Phoenix - so at least they were going to give me the phone for my trouble.
September 2015: Ported to T-Mobile. Had to trade phone in, so it was just an easy thing to upgrade to the 6s+.
I much prefer the physical size. Battery was never a consideration as long as it lasted as long as my iPhone 5 had.
Ok the reasons why I bought the 6 plus specifically were because of the larger display, the 1080p resolution, that it was available in 128GB of storage and the excellent battery life.
I came from android and had been using large screened phones with high resolution, expandable storage and removable batteries since the original galaxy note in 2012. I left the iPhone in 2012 primarily because I wanted a high resolution phablet with expandable storage.
So to switch back to the iPhone it had to have a large enough display, with at least 1080p resolution and enough internal storage and battery life to offset the fact that the memory couldn't be expanded and the battery was not removable.
After seeing the latest Sports Illustrated plus model cover, I knew I had to have a 7 plus phone. I appreciate the bigger and better screen, along with the longer battery life. Thus far, I like the 7plus as much as I did my 4s.
I got the first 6 Plus which was a dog performance wise but I love the big screen and battery life. I traded to the 6S Plus and it's been the best iPhone I've ever had. I would consider trading in the fall if the new version supports the Pencil. Otherwise, I'm a happy camper.
I got it because I wanted the bigger screen. The other bonuses are nice to though: longer battery life, slightly higher resolution (though honestly I don't really notice it unless I'm comparing the two sizes side by side), OIS on the camera (I have a 6S+ so no dual camera, though that seems like a pretty drool worthy feature).
I actually eventually ended up selling my iPad because my phone is big enough to do the tasks I'd do on an iPad, and when it's not I just pull out my computer.
I originally went to the Plus size with the 6S+ and continued the tradition with the 7 +. The plus has the better camera which is important to me (tend to leave the SLR at home now), battery life increase, better RAM specs with the 7, and a big reason - eyes. I started to have to wear reading glasses and with the larger screen, can use a larger font without sacrificing that much info so I may be able to read without the glasses.
I went from 6 to 7 Plus. Initially I opted for the 6 because I wanted to try it out and not go too extreme too quick in case I ended up hating the huge size.
Anyway, eventually I really started envying the Plus models. The size didn't feel unreasonable. It felt like a breath of fresh air actually. It made it a pleasure to watch video and play games. Battery seemed WAY better. Extra landscape features. Extra camera features. Etc. All of that played into my decision, and I'm glad. I love my 7 Plus.