Basically, if you are very high income or very good productivity and you work on the plane or the business class trip will result in immediate work on arrival, you can justify it. Otherwise, it's mostly for comfort.

If you are young, you can sustain the torture of economy class and still work on the plane and on arrival.

When I was young, I flew from the US non-stop to Singapore, arrived at about 6 am, got to work at 8 am. I flew premium economy, which was an economy seat with a little more leg room but not as much as domestic first class.