Choosing the best string tension of a badminton racket is a science in itself. The right badminton racket string and tension depends on your level of play, style and technique. As a general rule you can state that low string tensions are the better choice for beginners while high string tensions are suitable for advanced players with good technique.
The reason for this is that the higher the string tension is, the more the sweet spot decreases. And a smaller sweet spot leads to more miss hits from beginners, because they have not yet developed the needed technique.