Different gamma for different environments

[Anton Meleshkevich]

Let's imagine I just finished color grading of feature film. I worked at calibrated 2.4 gamma 100 nit monitor in environment with around 5-10 nit environment lighting.
Then I want to make a trailer for youtube. I've read a lot that I should to add a transform node after all the corrections and set input gamma 2.4 and output gamma 2.2.
This will make an image darker to compensate gamma 2.2 screens of iPhones (they aren't sRGB gamma). So the image will look the same on monitors with different gamma.
But why should I compensate it? Different screens gamma are different because of different environments they typically used in. So why should I compensate it?
Same thing with cinema projection.  They have 2.6 gamma because of dark environment. So why should I compensate it by transforming my image to gamma 2.6 and making it brighter? Won't it too bright for cinema theater? I thought, image should be the same. And different gamma of different screens will adopt my image to the environment. But if I transform gamma, this transformation cancels gamma of a screen. So it doesn't fit its environment anymore.

Edited May 11, 2019 by Anton Meleshkevich

[Emily Haine]

If you want to make a trim pass for YouTube watched on a mobile device or whatever, simply turn on the lights and make a simple trim pass at the end. Some people tend to be completely obsessed with gamma, numbers and complicated things too much.

[Jussi Rovanperä]

I don't worry about viewers gamma and viewing conditions because those are out of hands anyway.

What is important with many projects is to make sure that the grades work also on smaller devices like phones and tablets, something that looks moody on a big TV might just look really dull on a small screen, so one would need to find a compromise that works on both.