Manufacturer's recommended maximum tension
If you string over the manufacturer's recommended maximum tension you are doing so at your own risk! The maximum recommended tension can usually be found on the racquet frame, or in the racquet specification online.
The higher the tension you have, the quicker your strings are likely to break. Also, the more pressure you put through the racquet and significantly increase the chance of the racquet frame breaking.
The higher the tension you have, the lesser repulsion. This means you need to add more power with your wrist. With high tension racquets you need a faster swing speed and quick flick of the wrist. It will also have more chance to cause injury to your arm. This can possibly cause lead to tennis elbow (common elbow pain from racquet sports) and damage to your triceps muscle.
As string tension increases, the sweet spot on the string bed becomes smaller. This makes it more difficult to make contact with the sweet spot. If the shuttlecock misses the sweet spot, your badminton shot will hardly have any power.
*Tension beyond manufacturer's recommended maximum tension, the warranty will be voided most likely.