this is a touchy subject many will say a vast array of different things but i will tell you from experience that pruning is ok it may slightly stunt your final amounts but it will not be that bad.
the way i see it if the plant is in flowering and the lower buisness isnt getting the light that the rest of the plant is it is ok top prune you are trying to grow bud at this point and having leaves in the undergrowth just hanging around is diverting energy that could otherwise be used to pump up your buds.i always trim my plants starting with the bottom shaded leaves and then working my way up making sure all budsite have a nice ray of light hitting them all the time...