The purpose of a birth plan is to communicate your wishes for labor and birth to those who are caring for you. Writing a plan will help you to address different aspects of the labor, such as methods of pain relief and who you'd like to attend the birth. It also gives you a chance to ask questions about procedures such as induction and other types of medical intervention. Filling in a plan is also a useful way for your birth partner to be made aware of your wishes so that he or she can communicate these to the doctor while you're in labor.
Bear in mind that circumstances may dictate that not all of your preferences are met, but there's more chance of you getting the labor and birth you want if you've thought it through and written down your views. Being as informed as possible about labor and your choices (see Planning for your Birth) will help you to prepare in advance.