Thank you very much @Joerg. 
To be fair, neither have I. Every time I get to learn it from somewhere, I always get confused and eventually put off to use it. So, when I did further research and experimenting on the HSL model, I felt dumbfounded by how easy it was to use.
However, this is my personal experience of why I have never used it before. But, I do wonder that despite HSL is so simple, why has HSL failed to attract the attention of everyone else. Could it be a lack of information? Or, the way it has been explained could be improved?