If you are going to defoliate to improve the overall light penetration, my recommendations are to remove only the leaves, or sometimes just a lobe or two, that are covering growing points tht they are shading. By maximizing the growth points that are getting direct light you will be maximizing your yield later down the road. By taking only the minimum amount of leaves off to do this you will allow the plant to continue to use the other leaves to generate energy without cutting back too much of the energy they are making. A wholesale defoliation will remove most leaves and the plant has no way to generate the energy and photosynthesis it needs. It's a balancing act between too much leaf removal and promoting growth and growing points (the term I use for the end of stems and branches where the new growth occurs). During flowering, the difference will be more apparent as buds grow in direct proportion to the direct light they get. The larger growth points from vegging turn into more and larger bud sites during flowering, and the more light the bud gets, the bigger it gets. This is the ultimate goal that you should keep in mind. Don't overdo it and you will be fine. Even if you overdo it, the plant might stall a little but shouldn't be hurt unless it is very extensive.
