My wife is currently teaching English as a Second Language to mostly Taiwanese, Korean and Chinese students.... all online. Her students are almost all professionals in their 30s and up. After work they can log on from home or the office and study with her at their own convenience. So instead of reading a book or learning from someone in your own country who was a student at one time, you can study with a native speaker, thus learning at a much faster pace. Aside from the benefits to the student, it's also great that the teacher can work from home!