This has been a long discussed topic in my industry- coaches and therapists the world over have been offering their views on stretching since the creation of modern sports medicine in the 1950’s. So on that note- this is only another another view from myself as a coach, there are various scientific articles that you can read should you want to know more.
The Quick answer
It is an important part of a trainees’ routine and flexibility defined as “the ability for the bodys joints to be strong through their full range of motion”. With this is mind, it is important that flexibility is taken into account- otherwise you will not get stronger as intended.
Of course the image you may have is of people lifting one leg onto a park bench and painfully stretching their hamstring after a run- this is not necerssarily what needs to be done. There is a difference between dynamic flexibility and static flexibility- and when each should be targeted.
This can also be referred to as “movement efficiency”. How easy your body can move through its designated patterns, can you squat, hip hinge etc. A decent flexibility session can be of a dynamic nature and doesn’t have to be forcing your body through painful positions. Dynamic flexibility is encouraged before activity, as you are preparing the joints to push beyond their range of motion during the session. Static flexibility is encouraged post exercise as this is when you focus on specific joints to encourage developments in active flexibility. An example video is shown below on the types of exercise you can include in a dynamic warm up.
Static Stretching has been shown to reduce force production in Athletics before exercise, with this is mind it makes sense to perform this type of stretching after exercise- which is when we are more focused on repairing muscle tissue.
I hope this offers some useful information, if you have any other questions feel free to leave a comment.