Lower body flexibility routine with many excellent stretches, best suited for intermediates and advanced.
Here is a great lower body routine to incorporate into your fitness regime. It's best suited for intermediates and advanced who already have built a solid baseline of strength and flexibility.
Stretching in general is a great way to add range of motion to your muscles and thus allow them to perform better.
Strength & mobility should always come before stretching. Read this to understand what is mobility. Once the muscle is already strong and healthy, it can be stretched to increase its potential (range of motion).
Active flexibility is the best of both worlds, because you are building strength and flexibility at the same time by first stretching the muscle and then building strength in the stretched range of motion. You can find all active flexibility drills for the lower body in the Movement 20XX training course.