A birth plan is your advocate!
If everything goes smoothly, you have a list of suggestions to help you cope with the pain.
If you want a fan, a chance to go into the jet tub, or want to sit in the shower on a birthing ball put it on the list! lol
If something comes up, you are already well informed of any necessary intervention that may take place, hopefully leaving you more relaxed.
If there is anything important to you such as who will cut the cord or announce the sex of the baby, put it on the list!
Best of luck I hope your labour/delivery goes well