Flexibility is helping preventing injuries and helps by movements. If you for example can stand on one leg and raise the other behind your head it will clearly make a lazy vault much easier then if you can raise your food barely above the ground. It also reduce injuries from acciedental over stretching during a movement. Therfore two types of stretches are importand. One type is to be flexible during a training whereas the other are for increasing flexibilety. This means that the first type should be part of the warming up for a training whereas the second one can be seperated from a training. Moreover it is importand to stretch in order to keep flexible as strengthening the muscles also means shortening the muscles. This in turn increases the tension in the tendons which can lead to injuryes like shin splints.
For the warming up dynamic stretches are recomended. After a warming up static stretches can be practiced. This streches should be hold for 30 to 40 seconds and it should not be bounced. After a training some easy stretching should be done to lossen the muscles. After a bit rest or even the day after static stretches should be done to stay flexible.
In the following clip Awsa Bergstrom explains more about why stretches are nessessary and more.


The following playlist shows some ideas for stretching.