Plyometrics are a great way of training, but all depending on your goals.
Plyometrics involve jumping of all kinds, and the spring you have in your muscles and joints is important for health and overall performance.
Children in particular love plyometrics, and will often benefit from jumping exercises in their programme. This will only add to their development and move them on several levels, and allow them to perform in sports far better, increasing their performance significantly!
Then you have individuals who practice plyometrics in their sports training.
Professional athletes in particular become very good with their plyometric training, which produce increases in dynamic performance, ability to jump, become faster, stronger and more resilient to injury.
The problem starts when plyometrics are applied to all sorts of people, no matter if they have issues with their joints, or a bad knee, or a bad back or ankles, or all of these!
I have heard many horror stories with fiftysomethings being made to jump off boxes of different heights, causing massive stress on their back and knees, and ending up needing hospital treatment because of it!
What about jumping up and down with weights in your arms, they can be destructive for your joints if you have a weakness of any kind. Again, i am talking about those with a prior condition or weakness to this type of training.
The bottom line is to be careful with your training, try and avoid high stress to the joints movements, keep it impact free when possible and this will make sure you train for the rest of your life with little or no injury.
Trainers who preach plyometrics for everyone can be dangerous individuals, who can cause significant harm and injury to unsuspecting trainees. A little knowledge in the wrong hands can be highly dangerous!