Stretching is a commonly seen thing, sadly, when asked, people think they're doing it to prevent injury, while in some cases the risk of injury after stretching increases.
Let me explain what stretching is, what it does and what's it for. Stretching basically helps maintain normal range of motion. It can also help fix muscle inbalances.
Stretching does not prevent injury, which usually occurs during normal range of motion, why would widening the range of motion help prevent injury?
Stretching reduces the strenght of the muscle in it's tensed form, meaning you can get easily hurt if you do lifting after stretching. I suggest you warm up, not stretch, these are two different things. Some people also stretch after the workout, saying it will reduce the soreness, which it actually does not.
The reason why people think stretching prevents injury is because they're confusing or mixing it up with warming up. Warming up does reduce the risk of injury and in fact, greatly.
With stretching you can also fix muscle imbalances, it's a wide subject, so I'll do an entire daily of it someday. Muscle imbalance is basically one or two big muscles doing the work for other, smaller, weaker muscles. For example your bicep and pec minor doing the work for your lower lats while you're doing pull ups, that's a really common one. How do you fix that? You stretch out your arm entirely before doing pull ups, stretch out both of your arms against a wall as far as you can - ofcourse, don't injure yourself. If you do this, the smaller and weaker muscles will start working, instead of letting the bicep and pec minor take over the work completely.
So, what is stretching good for? It is good for decreasing imflammation and increasing the range of motion, allowing you do reach better, or sit on your straight leg. There are many more uses for flexibility too, ofcourse. I see a lot of people not doing the stretching properly, you can actually injure yourself while stretching the wrong way. So how do to stretch the right way?
To stretch the right way, first of all warm up, and then cool down a little bit. You should choose a stretch and do it so you feel pulling in the muscle - don't go into the pain zone though. Many people get this part right, but they bounce or do the same stretch repeatedly in a few seconds, that is plain wrong. Once you get into the position, that right spot, you should hold and continue to hold for atleast 30 seconds. Then release. Once a day is enough, studies shown that three stretches of 30 seconds a day had the same result as one stretch of 30 seconds per day. If you're doing it right, your flexibility should increase in about six weeks, if it doesn't, increase the hold into around 60 seconds. Don't increase if you see improvement though! You shouldn't expect too much because it is, afterall, a slow process.
Besides improving the range of motion, stretching can be relaxing (exmpl. joga). I'm hoping this cleared up the misconseption of stretching and now you know!