@tinkerbell
Endrocrinology is a very complicated medical field, so take anything you read on the internet with a grain of salt. Even specialists have differing opinions, and very commonly. With that said, I do cycle. I don't know what would be the difference between doing it or not in me, as I haven't done a non-cycle HRT. Myself, I merely try to mimic what goes on in women who have working ovaries. When I take medroxiprogesterone I notice I get a bit crank, my breasts swell and hurt, so it is basically the same as having PMS. About two days after I stop taking them, my mood gets back to normal. I have been having good brest growth, better than I expected and they are beginning to look round and not-conical, and many facial changes.
But each individual body answers on it's own manner to HRT. Even though my cycle works for me, there is no reason to believe a cycle works for you.
If you want a medical opinion on why there is the use of progestagens for women, the best person to ask is a doctor. Over here, it often boils down to many contradictory opinions and links to studies that aren't quite validated by the medical community.