I see many people doing fairly-aggressive stretching before sports or a weights work-out. Wrong. Except for calf stretches, which are a good idea.
A warm-up for a sport or weights is a 5-minute jog, elliptical, or calisthenics things like jumping jacks. Stretching cold muscle is a bad idea. You can actually hurt yourself that way.
Stretching after a sport, a calisthenics hour, or weights might be a good idea or maybe a waste of time. If you take a calisthenics group program in a gym, you will see that they spend the last 5 minutes or so doing stretches on the floor. That feels good, if nothing else.
10 Best Stretches For Your Whole Body After a Workout