it is challenging to answer a question about benefit when the intention and benefits are not clearly stated. You say a primary goal is increased flexibility. This is best pursued through a stretching routine, stretching class or the like. If one's intention is stretching these avenues are more efficient and direct for that (stated) purpose.
Yoga is lived it is not performed. Therefore it is "done" all day long. Asana (poses) are a tiny fragment of Yoga.
Ahhh but you seek a pragmatic answer. In the yogic context asana serves a purpose. Based on my studies, practice, teaching, et al that purpose is not stretching though it is completely possible that stretching is a by-product.
Muscle tissue should not be overly stretched. Presuming we are talking about asana (only) it is about stabilizing some things and mobilizing others. Therefore even in a context where we could agree it is about muscle fiber it is still not about flexibility. Becoming overly flexible is dangerous. In fact any seasoned yoga teacher will tell you that students who are too supple are at greater risk for damage than those who are stiff.
If after all this you are still focused only on flexibility AND you chose to utilize yoga asana for that purpose, then I'd advise a slow, gradual practice absolutely NOT over stretching or overdoing. Flexibility (of body and mind) have some value. Being overly attached to that flexibility (without a purpose for it) is actually counter to yoga itself.