Ya I get that I guess I just don't think it will diminishing that much. Here's my logicAgain, to a point of diminishing returns. See the graphic I posted above; the last little bit is costly in terms of both light and environmental control and doesn't return an awful lot for the trouble.
4x8 room 1000w let's say you have a really good grow and get 1.8 g/w that's 1800g now put 1500w in the same space diminishing returns brings you down to 1.3 g/w that's 1950g over a qp extra is worth it to me that will cover the electricity cost for the whole grow. Maybe I'm wrong but if I manage at least 1.3 g/w this grow I'll be super happy with my decision. Another reason to run more light is to add heat to the room in my space if I ran 30w/sqft I would need to run a heater to get my temps up