The general idea is it eliminates the sexual componant from the equasion. HRT also effects the mind and allows you to make an informed decision on wether or not that continuance of transition is right for you. You can stop and transition back at anything while on HRT but after 3 months there are irreversable changes such as breast development, and reduced/elemination erectyle function and a host of other issues. Of course indivudual results will vary.