Using specific stretching and self-releasing techniques to improve your range of motion, in combination with your strength, will give you the benefit of moving your limbs (arms and legs and even spine) through range; for example, being able to raise your arm right above your head or even how far you can perform a side raise with your leg.
Reduced flexibility can cause parts of the body to sit in sub-optimal positions making it difficult to perform quick sudden movements/perform in high intensity classes. This results in further pain and stiffness and is usually the cause of injury/re-injury.
Mobility will allow you to perform tasks through range with no pain, repetitively through your weekly schedule. It will also allow the body to recover and repair before your next hit out!