1) It gets the birthing person and their partner/support people on the same page.
2) It's a great tool to share with your hypno-doula so she can work to help make this birth YOUR dream birth. A good doula leaves her personal preferences at the door and works hard to help you achieve your goals.
3) Despite some concerns to the contrary within the birth world, in my experience health care providers, especially nurses and midwives, DO read them and try to help their clients get as many of their preferences as they can.
Check out this amazing birth plan one of my student recently created and scroll down to read why I think it's amazing!