I graduated half a year early and can honestly say it was one of the best choices I've made in my entire life. That being said, it is definitely not for every one. You should have a plan or goal that you want to complete in the time that you would normally be finishing up school with, not just to bum around (which it doesn't sound like that's what you want to do anyways). I was lucky enough to be granted the opportunity to travel and volunteer in Africa with my family for three months. This was an incredible experience and really helped me learn more about who I am and what I want to do with my life.
People say senior year is the time of your life, which it is, but you don't need to be constrained to family, friends and school to make it that way. You are young and energetic and have the world at your fingers so make sure you find something you would really like to do, or a place you would really like to go. I definitely had fun the first half of my senior year and was glad I stuck around for that, but to be able to explore the world was eye-opening and posed challenges I wouldn't have faced otherwise. Also, it gave me the necessary break between education for me to be motivated freshmen year at college.
Like I said, it definitely isn't for everyone, but if you feel strongly about going out and DOING something I would highly recommend it.
Feel free to pm me any other questions you have about the experience.