i heard that estrogen and progesterone virutally prevent other hormones, lh / gnrh, etc.. from being produced. i don't see the benefits, why is this so needed

Not sure if you are talking about a male or female but here is info in female hormones the rising estrogen levels in the plasma exert a negative feedback on the hypothalamus and anterior pituitary inhibiting release of FSH and LH while simultaneously prodding the pituitary to synthesize and accumulate these gonadotropins.