The goal of a parenting plan is to focus on you, your ex, and your child. It's made to be simple and easy to use. Divorce is already complex enough; a parenting plan should be written with everyday language and lacking legal jargon and confusing terms. It's not made for the court, but for the parents.
The plan's goal is also simple: It seeks to create the best situation possible for the child. You've probably heard people talk about a child's "best interests." The plan is designed to put them at the forefront and address what the parents want later.
For example, both parents may want custody, but one parent may realistically be far better suited for it than the other. Perhaps one parent travels out of the country all of the time for work, for instance, and would have to hire a nanny to watch the child. Even though that parent wants full custody, the courts may decide that the other parent should get it because that gives the child the most stable home life possible. The other parent can then be given visitation rights so that the child is involved with both of them -- something else that courts favor to help the child's development.
This is just one example, and there are many factors to consider in every case; it's not impossible to get custody because you travel often. However, it does a good job of showing how the child's best interests will trump the parent's desires.
Some would say that the parenting plan is the most important document that you're going to take away from your divorce, even though you may be more focused on splitting up with your spouse. Be sure you know how it works and what rights you have in Tennessee.
Source: Tennessee State Courts, "About the Parenting Plan," accessed May 26, 2016