Stretching is so often something people neglect to do at the end of a training session because they are usually too tired to do anything else.
Also we have seen people RUSH through each stretch and this totally doesn’t allow you to get the full benefit of stretching.
Why do we need to stretch?  It is to improve our flexibility, the range of motion that is available to our joints. Flexibility is important because:
It improves muscle balance around a joint, thus improving posture, It also reduces the chance of injury when playing a sport or in performing our every day activities.  Flexibility also increases the blood and nutrient supply to muscles and cartilage, which helps in reducing muscle soreness after training.
Stretching should not be done as a warm-up before working out, you could risk injuring your muscles if stretching them when they are cold.
The best way to warm up before a work out is At least 3 to 5 minutes of cardiovascular training.
At the end of your workout is where you should be stretching.
Each major muscle group should be stretched slowly and with control, holding each stretch for 1 to 3 minutes. Remember, hold each stretch at the point of mild tension or tightness, not to the point of pain.  
The reason It’s so important to stretch after doing any physical activity is because during exercise when muscles perform, they tighten and shorten as a result of your workout. Stretching helps to restore and improve their length.
Make sure your stretching properly after your workouts!