As with many fitness questions, it depends on how you define plyometrics. Academically, it implies that you take the targeted muscles (quads, for example) to the point of maximal stretch, then vigorously contract the targeted muscles to accomplish their typical movement. For example, if you jump off a 12 inch bench, especially if loaded with a barbell or dumbells, into a position of knee flexion (which stretches the quads), then jump as high as you can, knee extension as a result of quad contraction is the primary mover, gastroc-soleus, gluts are secondary. In other words, ankle plantar flexion and hip extension are secondary to knee extension in this example.
The benefits of this type of training in power and performance training are undeniable. In a general fitness training program, however, the key concern is the current fitness level of your client. I’m not an advocate of true power plyometrics for an untrained client, as the adaptation of connective tissue (ligaments, tendons) is most likely not sufficient to withstand the tissue stress.
Modified plyometrics can be used in most any training situation. Just jumping up and down, for example, can be considered to be a form of plyometrics. The benefits are the exercise stress to the tissues involved to stimulate them to adapt and become stronger. Doing a pushup where you have your client push up off the floor with both hands until the hands are off the floor, then come back down into shoulder horizontal extention and elbow flexion and repeat the movement is a plyometric exercise.
The long term benefits….power. Work through a distance over time. The trail down is a greater resistance to the stresses of endurance exercise…running, cycling, cross-country skiing, swimming, and on and on, not to mention strength and power weight lifting.