Why take college courses while in high school?

A Q&A from the San Francisco School of the Arts' College Bulletin, by college counselor Gordon Chalmers:

Will taking college courses while in high school help me get into college?

Definitely yes, but sometimes getting to take these classes can be difficult, as first priority goes to current students enrolled at that college. Lowest priority goes to high school students. In many cases a college-level course counts as one year of a high school course (i.e. taking trigonometry at college for one semester counts as one year of high school trig), plus the grade earns an extra point in the GPA calculation the same as taking an AP or Honors course. Also, colleges love students who have successfully completed a college course, as it demonstrates that you can do college-level work. All local community colleges offer courses for high school students during the school year and summer. Go to that college's website and look for the Concurrent Enrollment Program.