The Importance of Stretching 
It's not just enough to build muscle and achieve aerobic fitness that great but, you need to think about flexibility, too.
You may think of stretching as something performed only by athletes, runners or gymnasts. But we all need to stretch in order to protect our mobility and independence, especially as we age. A lot of people don't understand that stretching has to happen on a regular basis and is the best on a daily basis.
Why stretching so important
Stretching keeps the muscles flexible, healthy and strong and we need that flexibility to maintain a range of motion in the joints. Without it, the muscles shorten and become tight. Then, when you call on the muscles for activity, they are weak and unable to extend all the way. That puts you at risk for joint pain, strains, and muscle damage.
For example, sitting in a chair all day results in tight hamstrings in the back of the thigh. This then can make it harder to extend your leg or straighten your knee all the way, which inhibits walking. Similarly, when tight muscles are unexpectedly called on for a strenuous activity that stretches them, such as playing soccer, they may become damaged from suddenly being stretched. Injured muscles may not be strong enough to support the joints, which can lead to joint injury.
Regular stretching assists in keeping the muscles long, lean, and flexible, and this means that exertion won't put too much force on the muscle itself. Healthy muscles also help a person with balance problems, thus assisting us to avoid falls.
Where to begin
As our bodies are full of muscles, the idea of daily stretching may seem overwhelming. But you don't have to stretch every muscle every day. The areas critical for mobility are in your lower extremities which are your calves, hamstrings, hip flexors in the pelvis and quadriceps in the front of the thigh. Stretching your shoulders, neck, and lower back is also beneficial. A good goal would be is to have a program of daily stretches or at least three or four times per week
It is best to seek advise regarding your muscle strength and have tailored stretchening program to fit your needs. If you have chronic conditions such as Parkinson's disease or arthritis, you'll want to clear a new stretching regimen with your doctor before you start.
The increasing collective effect of stretching
Stretching once today won't magically give you perfect flexibility. You'll need to do it over time and remain committed to the process. It may have taken you many months to get tight muscles, so you are not going to be flawlessly flexible after one or two sessions.. It takes weeks to months to get flexible, and you'll have to continue working on it to maintain it.
Appropriate execution
We used to believe that stretching was necessary to warm up the muscles and prepare them for activity. However, mounting research has shown that stretching the muscles before they're warmed up can actually hurt them. When everything is cold, the fibres aren't prepared and may be damaged. If you exercise first, you'll get blood flow to the area, and that makes the tissue more pliable and amenable to change. All it takes to warm up the muscles before stretching is five to 10 minutes of light activity, such as a quick walk. You can also stretch after an aerobic or weight-training workout.
Hold a stretch for 30 seconds. Don't bounce, which can cause injury. You'll feel tension during a stretch, but you should not feel pain. If you do, there may be an injury or damage in the tissue. Stop stretching that muscle, and talk to your doctor.
Stretching before physical activity affect performance. 
There is no clear evidence that is does assist to prevent or causes injury. There is an abundant of articles on the subject. Below is just a few and you can make up your own mind.
https://bjsm.bmj.com/content/34/5/324
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1250267
https://www.abc.net.au/news/health/2017-03-02/does-stretching-help-prevent-injuries/8313574