Once again I hear people asking "Why would a student want to get high school credit for classes taken in middle school?"
This may not surprise you, but you're not going to get a good answer to this question from someone who isn't interested in it or who thinks it ranges from pointless to being a bad idea. Yet that's who have been answering that question of late.
So, rather than their explanation, to graduate high school early, let me instead offer some better reasons.
1) Lighter course load when taking challenging classes. A high performing student might take as many as three or four AP classes as a senior. These classes are challenging and demanding classes. Wouldn't it be nice to have the option to not take two other classes at the same time so the student can devote more time to the AP classes?