One thing to remember is that Idaho is pretty large in land-area and pretty small in population. There are lots of small towns with really small schools.
One thing this will help enable is kids in these small schools being able to take a wider variety of courses, or more advanced courses that their local school district simply can't afford to offer. Imagine a high school so small that there is only one "science" teacher for all science subjects. Now imagine you're a kid in that school and you love physics and would like to take AP physics so you can get a leg up going to college.
In Boise (over 100k population) there's no problem - there are plenty of teachers and plenty of courses. But if you're in Twin Falls or an even smaller community (like the one Napoleon Dynamite was set it), you're screwed as a kid.
Another thing to consider is that for everyone, the future of education will be web-delivered courses. If you've ever done one, you'll know that courses delivered this way require a different kind of discipline than a "forced to sit in a seat" class. If you agree that the idea of k-12 education is to prepare students for life, then it makes sense that part of the education process is to teach kids how to learn using this relatively new method.
By requiring it of all schools (large or small), it forces the issue of establishing the infrastructure to support it and it also helps level the playing field for kids who are at a geographic disadvantage.