We have opposing muscles around a joint. Opposing equal force from both muscles is needed to keep the bone centered in the joint during motion. When one muscle is weaker than the other, it causes muscle imbalance leading to injuries. Also, when a muscle is too tight, the joint tends to move in that direction, away from the opposing muscle
The quadriceps and hamstrings are the 2 muscles that surround the knee joint. If the hamstring is weaker than the quads , the knee cap ( patella)could get damaged. If the hamstring is very tight, it will not allow the knee to extend fully. This puts pressure on the quads and knee joint, leading to injuries
Do a whole body workout, involving opposite muscles. Concentrate on doing compound exercises that involve multiple joints, than single joint exercises.