Meniscus acts as a natural spacer between femur and tibia thus protecting the articular surfaces of the knee joint. Functions of meniscus are:
Acts as a shock absorber
Distributes axial load
Increases stability of the knee joint
Provides nutrition and lubrication to the knee joint
So preserving the meniscus is important since its absence may lead to increased contact stresses on the articular surface thus leading to its damage and subsequently leading to early osteoarthritis
Repair of the meniscus is important because as the tear progresses a due to abnormal stresses on the knee joint, a part of meniscus may flip or detach itself and forms a loose body which causes locking and persistent pain
Moreover tears in the inner portion (white zone) of the meniscus lack in proper blood supply and are less likely to heal on their own hence require repair whereas tears in outer portion (Red zone) do heal on their own and sometimes require repair.