I start selectively trimming my fan leaves late in flower - only those that are really blocking decent bud sites though.
I run a perpetual harvest with a 10 day cycle, so I get lots of opportunity experiment. Nothing formal (yet anyway), but I see that opening up the canopy with selective trimming gives much fuller bud all the way down the stems. Sure fan leaves absorb light, but so do bud leaves.
I'd tend to agree with the mother nature argument if I were growing 12 footers outside on a hill. I don't - I grow inside and do all kinds of unnatural things to my plants, bending, potting, feeding etc...
I do what I see producing bigger and better buds.