Isometrics are one of the most underused training methods for creating high amounts of tension and stress in the muscle. Isometric training produces a greater level of activation than any other type of contraction. One of the main benefits is that the body is able to activate nearly all the available motor units, something that's usually very difficult to do.
Isometric holds also increase joint stability, improve reversal strength, and may be helpful in rehabbing injuries. It's also great because it can help you develop a stronger mind-muscle connection.