I understand what you mean. Of course for any kind of coding work best option is desktop/laptop. However, tools like this can be beneficial when computers are not available and for quick on the go tests, code review, etc. Emphasis on this one though is more for educational purposes to learn little parts at a time. Also, using on mobile can give access to test mobile features, certain mobile hardware, sensors can programmaticaly be accessed. In the end it is not a replacement for computer IDEs but rather an additional tool that can be helpful when needed.