One of the biggest debates out there. However, I can speak from experience. I had 6 big buds under 600watt hps lights on 12/12. I cut all the fan leaves on 1 of the 6 plants to test this theory. I found that the buds did stretch but were very thin and had very little weight on them. Also, my bud was a little more harsh on that one, possible due to chemicals not being able to exhaust via the fan leaves. In all, the plant weighed alot less than the others and didn't taste as good.
I would keep the fan leaves on the plant and only take them off when they turn very yellow and are half falling off anyway.