One of the things I have learned in the process of losing weight and getting fit is that as important as it is for me to make healthy food choices and get my workouts in, it is also important to allow my body to rest so that it can fully recover from the workouts I am putting it through.
A mistake I've made in the past is to go full on working out (jogging, workout DVDs, etc.) everyday to the point of burnout then it is several days (sometimes more) before I feel like doing it again. This is a mistake made by many when they are first learning to balance healthy living and exercise, with real life. What ever program you have chosen to follow, whether a running program or CrossFit, it is important to take a rest day and listen to your body as you go along.
Keep in mind a rest day does not mean a "cheat day", keep your choices healthy, but make sure you rest your body thoroughly.
So wherever you are in your fitness plans, make sure to get your rest day in, your body will thank you and you may even reach your goals faster.