I don't think we place as much importance on stretching as we should. Stretching in itself is not some tree-hugging "let me just sit here and breathe" type of activity. If you exercise intensely and regularly, stretching can be pretty painful. That should tell you that your muscles get tenser and tenser and need a release, however painful or boring it might seem.
So one big question is: "Why stretch?". When you work out intensely, especially when you lift weights, you muscles go through a contraction and relaxation dance. This causes muscle tissue breakdown and requires you give them time to repair. It's that constant breakdown and repair that causes your muscles to grow.
If you are not dedicating adequate time to stretch, usually, your muscles do not repair as quickly or as well as they could, and you may be in more post-workout pain than you need to be. Your muscle fibers may not be properly aligned for them to repair properly, which means they may not grow as beautifully as they could have if you did.
Increasing Flexibility and Reducing the Risk of Injury
Stretching your muscles also increases flexibility and reduces the risk of injury by ensuring that you are putting pressure on the right muscles when you exercise. For example, the more flexibility you build, there might be a lower probability that you hurt your joints when you run. This is because you put more pressure on your inner thigh muscles than your outer, which means less impact on your knees.
Now, this doesn't all mean you should ignore posture during exercise and just stretch after, and everything will be okay. No. Posture is very important to ensure you are putting pressure on the right muscles. But that is a story for another day. Even as you stretch, posture is important to increase flexibility. But be careful, more flexibility may mean less pain during stretching, but it could also mean misalignment of joints if you don't pay attention to your joints because your body allows you to do things it may not have before.
Reducing Post-workout Pain
Stretching helps to reduce post-workout pain by aligning your fibers appropriately. It doesn't take it all away (you did just tear down muscle tissue), but it makes you feel it less.
I don't think people realize that stretching in itself is part of your workout. This is one of the foundations of power yoga. You do require your muscles to hold you in certain positions, which is part of the reason why yoga aficionados have pretty toned muscles.
So stretch it out after you've warmed up (don't stretch 'cold' muscles) and after your work out. Thank me later :)
Cheers Eights & Weights!