just like with the nute companies recommending more than you need...
I think the market has been geared towards dudes building out grow houses and slangin' units.
More light means more nutes means fatter flowers means more weight - that may or may not have the quality of weed not juiced on the Brawndo.
I like having more light available, but running them at 75% or less. I have roughly 300 actual watts in a 40" x 40" so about 100 watts per linear foot seems like it's enough. 200w for a 2'x2', 300w for a 3'x3' etc.