There are so many great advantages to doing an internship wether for pay or college credit when you are in high school. First of all it is a means to explore careers you are thinking about going into to see if that career fits you.
You work for a summer in an internship and not only do you get an education in your chosen field, it will also look great on a resume someday. If it turns out during the time you are doing an internship you decide not to go into this kind of career. You have saved yourself a tremendous amount of time and money not pursuing the wrong career for you.
You can read more about high school internships in the following article by Rachel Levy: