Thc production/trichome formation

I'm going into week three of flower and am being told to defoliate my plants and trim some under growth to get light to my plants. My question is, if I don't do this will thc form or trichomes form irregardless of the light hitting the plant? Is it super important to get light to the undergrowth since the light cycle of 12/12 makes buds form anyways?

its called sucker growth
i usually clip it before flower
yes they will still get trichs but there will be no density to the buds that arent exposed to light