G. Mark’s Answer
Most colleges will not accept you without a high school diploma in the first place. And even if they did, there will be courses in high school that prepare you for college and are not available in college. But here's the good part. Why would you want to postpone until college something you could have studied for free in high school and why would you want to miss that experience? I found that the classes I took in high school that I could have taken in college allowed me to learn more in college before graduation, since my classes in college could be that much more advanced.
Now, if you did find a situation where you could be admitted to college without having taken courses in high school, it seems you'd stand to lose more than you gained. So why bother? Get more prepared in high school!