Water Pan in Offset - necessary on larger cooks?

I will say no.

My research has said not on a large cook. Maybe on a small cook

I wold say it depends mostly on the cooker. On my buddies small brinkman offset it's pretty useful. But I have no need of it in my cooker which is much larger. I think it has to do with the mass and the proximity of the fire to the food. But that is just a guess. No scientific basis for that. Just a redneck that does a lot of bbq.