I haven't suffered in any way so far from the smaller screen. Many moons ago (2011ish) I used to code on an 11inch Macbook Air (Corona SDK, XCode, Sublime Text etc.) which was quite small and did give me eye strain and headaches after a while. Especially outside where I do enjoy working. But I do enjoy the light, small, go anywhere devices.
I run the Macbook at More Space setting, 1400x900, which is the standard screen setting for a 15 inch Macbook Pro.
So you get like for like in that respect. And whereas everything on the 15inch screen was a bit 'big', the resolution works well on the 12inch. The retina display helps enormously, keeping everything sharp and very readable.
Coding is fine on the 12 inch. Like I mentioned if it fits on the 15inch MBP standard screen setting then it fits the same on the 12 inch More Space screen setting.
Increasing the font size when coding is also an option for days when you are a bit tired or the eyes aren't working that great.
I guess at the end of the day it depends on what you are used to. If you spend most of your time in the office with a 2 or 3 monitor set up and are considering the jump to a 12 inch screen then you will find the process jarring.
However, if you, like myself, have lived on a 15inch MBP for the last god knows how many years and are tired of lugging around the weight or listening to fan noise a lot of the time then the MB will be a refreshing experience.
I'll let you into a little secret which catches a lot of people including briefly myself out.
When I went to pick up the MB from the Apple Store I was walking past the table with them all laid out and I glanced across and thought to myself "It's a bit small. How am I going to do anything on something like that?".
Momentarily I did think that maybe I was making a mistake and the MB was a bit of a joke to consider doing anything 'proper' on it.
But I'm glad I did buy the MB. It has been a perfect tool so far. Which can go anywhere, and most importantly you can create anything you want on it without the rest of the world noticing you have brought your serious laptop with you.
I'm not sure what the experience was on the 2015 model but on the 2016 MB I haven't found anything that hasn't performed similar or exceeded my expectations.
