Benefits of slow and controlled workout
In any free-weight exercise there are two basic motions. One is Concentric, or lifting phase. The other is the Eccentric or lowering phase.
During the lifting phase the muscle shortens and contracts. During the lowering phase the muscle lengthens. An example would be a Dumbbell bicep curl workout. Lifting the weight upwards toward the shoulder shortens and contracts the muscle. Lowering the weight to the beginning spot lengthens the muscle.
Studies have confirmed that lowering the weight is just as important as lifting the weight. Lowering the weight causes just as much muscle-cell damage as lifting the weight does. The muscle-cell damage and repair is how our muscles grow.
Hence every repetition must be done slow and with proper control. Also ensure that you lift weights appropriate enough to do the entire range of motion.
We often notice members lifting weights bigger than their physical capacity. This results in quick rapid movements with half the range of motion , leading to a completely non beneficial workout.