It is extremely important to stretch out especially after a workout. Stretching out will help to minimize lactic acid buildup, cramping, toxin build up in muscles.
It help to stretch out the fascia that allows the muscles to grow. They figure you spend 90 minutes in the gym pounding the muscles good and hard taking 10 minutes at the end shouldn't be an issue.
Also deep tissue massages once a month or so will greatly improve growth, healing and toxic buildup.