I defoliate all through my grow. Each time a budding tip is 1"+, i pull the fan leaf. In my tests i noticed no difference in bud size with fan or without. I do, however notice a HUGE increase in light down into the plant, and thus much better/thicker buds. On top of this, with defoliation, i actually end up pulling MORE leaves overall than before, so the plant is actually MORE vigorous. Also, i am able to use 1/2 strength nutes, saving lots of $$ with no fan leaves to suck them up.
my tests indicate that fan leaves help get the budding joints started, and provide a buffer for nutes. Otherwise they are just shading out the buds. Isn't getting light to the buds what it is all about?
Thus my tests go against conventional wisdom, and i'll happily continue to defoliate all the way through my grows. I highly recommend that you DONT do it, i mean what will you do with all those extra buds????