Static stretching after a workout is one of the most neglected parts of fitness. This is because stretching to most, myself included, seems so boring; holding painful positions, especially just after a workout is such a big effort. It is normal to feel this way, I still do sometimes, but what it comes down to is your goal, and in everyone's goals stretching plays a big part. For example, build muscle? Stretching is a must, you cannot build on top of tight muscles. Losing fat? Stretching is important, while you are on the cardio machines, or jumping up and down in a circuit, tight muscles can lead to injury. Improving flexibility? Static stretching is of obvious value. 

So after every workout you should aim to be stretching at least the muscles that have been used. This will help them relax and loosen, ready for the next workout.