How, When and Why to Stretch
As benign as the topic of stretching would seem to be, there is a lot of controversy surrounding its purpose and validity. To start, let's delve into the two most common forms of stretching; static vs dynamic. Just like the names imply, static stretching involves simply holding a stretching position for a given period of time; usually 30-60 seconds. Dynamic stretching, on the other hand, is moving your body though different positions and planes of motion which in turns stretches your muscles during the movement.
In general, the consensus in the "educated" fitness industry is that static stretching really isn't that helpful unless you have some specific flexibility goals in mind. Perhaps you have a goal to do the splits, then practicing some static stretches may be beneficial to help you meet that goal. Another possible use for static stretching is after a workout to help you return your muscles to their resting length and aid in recovery. But beyond that, it really isn't helpful for overall physical performance during a workout.
Dynamic stretching, by comparison, can enhance performance if used prior to a workout session. It should be short and concise, help to increase blood flow, raise body temperature, and lubricate the joints you plan to use. It's also important to choose movements that will help you facilitate the types of exercises/lifting you plan to do. (This gets a bit more complicated but explains why Myles chooses certain warm up routines for you to perform prior to specific exercise programs- there is a method to his madness!)
Another important point to address is the feeling of tension or tightness in a certain area. Often that feeling is due to weakness in the muscle, not lack of flexibility. For example, say you feel like you have tight hamstrings; you would be better served to work on strengthening those muscles then stretching them. We need to focus on stability before mobility of our muscles and joints to stay fit and uninjured.
And you don't have to just take my word for it. If you want to read a quick article where 5 fitness professionals were interviewed about their differing views on stretching, here you go.