The GED is a good alternative for two types of students: one who wants (or needs) to graduate early and one who dislikes high school and wishes to move on (to college, US Army, etc.). Sometimes, the same student both dislikes the high school environment and wants to graduate early, but a few people simply want early graduation so they can begin their next step in life, whether it's sports, a job, or non-academic interests--or, sometimes further education in a specific field. For students who aren't fond of high school, or have an intense interest in one subject (for example, music or art), the GED is a means to get to the next phase.
For example, an artist may want to begin art school or have an opportunity to travel in pursuit of their art. The GED means that student can finish high school a year earlier.
Other students find the social scene in high school uncomfortable and want to move on. The GED allows a graceful exit from high school, since passing the test proves the student has mastered English, math, social studies and science at the level of a high school diploma.