The bar is better than waving your arms and legs around. With the bar the lifter has to use the exact form he will during the actual work sets but there is not nearly enough weight to get the lifter tired.
The bar is the perfect stepping stone between walking/rowing general warm up and movement specific warm up. It sets the groove, gets blood exactly where it needs and doesn't fatigue.
Oh, by the way.
This. Weightlifting is a sport, not a very smart way to get stronger. Squat, bench, row to get strong. Play your sport to get better/faster in you sport.