As many people know, stretching has got a load of benefits. From helping to improve range of motion in joints, to recovery in muscles and better blood flow; a good stretch can be very helpful. However it isn't always the most beneficial way of exercising, and there really is a time and a place for it. Let me explain when I think it is worth doing, and when it isn't.
For me, stretching is best done when you are taking a rest day from other exercise, and want to do some recovery work on your tired muscles. By giving yourself a little warm-up to make sure you don't go into stretching too cold and tight, and then taking yourself through some stretches that will help tired muscles with recovery, you're not allowing the stretches to affect any exercise/hobbies you do, and you're avoiding risking an injury. This stretching will also potentially work on your range of motion in joints that are affected by tight muscles, therefore improving your posture and you'll be moving better in your exercises. Also, by doing all this on your rest days, you're allowing yourself to stay active (albeit it very activity) on your days where you might not do much activity. Therefore, in a roundabout way you start to burn more calories over the course of the week - which is a very nice added benefit that could help you reach other goals!
Another time that I think stretching is really beneficial is when you are dealing with lower back pain (LBP). Now LBP is a whole other topic where I could go into so much detail about different aspects that affect it, but essentially if your LBP is deemed as not severe and you can still get on with everyday life, then stretching is a very beneficial way to deal with LBP. Typically pain in this area is caused by tight muscles, and how can we improve tight muscles? We can stretch them out; see where I'm going with this... Tight muscles affect the range of motion at a joint, and bad ROM means that our posture and mechanics don't work properly. Therefore, if we can correct this, we can relieve any LBP and improve how we feel. Now typically when it comes to rehab work for LBP, we focus mainly on muscles that are tight, the main ones being: Hamstrings, Hip flexors and chest and shoulders. Recommendations are also to stretch 7 times a week as well, so plenty of stretching for you to do! Now of course it is best to get professional help and advice before doing any rehab, but hopefully this can help you build some awareness about how you can relieve any pain that you could experience.
The one main are that I don't believe stretching is good is before you exercise, whether that's before doing a gym session or before you play a sport, it isn't worth your while stretching before hand. Simply, I believe stretching before exercise can increase your risk of injury during your session. Other professionals may tell you different, and this is a topic that isn't quite black and white on the right answer, but for me it's not worth it. The main reason for this is down to elastic energy. When we do the negative part of a rep (going down to the floor in a squat) are muscles store energy in the muscle tendon complex. This allows you to then use that elastic energy in the positive part of an exercise (the standing up part in a squat). This helps a lot when we are doing power based movements like running and jumping, as this energy will help us to generate more out of the movement to go faster and further. Now if we hold a stretch for even as little 2 seconds, we can lose pretty much all of that elastic energy. Now imagine losing that elastic energy, and then trying to jump as far forward as possible. Firstly, we wouldn't get as far, but secondly we'd be asking a lot more of the muscles without any support from stored energy, which will risk causing an injury, which is something that no one wants. This here is really why I don't like stretching before exercise. If you feel like you need to do something in your warm-up, add in some dynamic stretches and mobility drills, as these will help your muscles get warm while allowing them to stay as explosive and risk-free as possible.
So there you have it, where I think stretching is and isn't beneficial for you. Of course, everyone has their own opinion based off research and qualifications they have, but for me, this is the knowledge I go off for my clients.