I've never been flexible even after doing years of martial arts. In fact I'm the opposite of flexible and this finally come to create a problem. My spine erectors and hamstrings are so tight that my pelvis tilts and causes pain in certain situations. I finally got into seeing a sports physiotherapist and he has had me doing some stretches, several times per day, to try to correct this issue. I guess flexibility in itself may not have a benefit, but I can tell you that being inflexible can be a detriment.