We like to grab 2 sets of weights since we can use heavier weights for legs and back, but we need lighter weights for arms and, especially, shoulders. (exercisewithextrafries.com)
Of course, do not use heavy weight at the beginning, but as you get better, you can increase the resistance slowly. (abmachinesguide.com)
Quite often, people have trouble locking out the top few inches of the movement when using heavier weight. (muscle-fitness-training.com)