Using video for background reference
Some animators say using video reference is cheating. Don't be fooled by that. Since the days of the Nine Old Men—the core pioneer animators of Walt Disney Productions who created classics such as Snow White and Pinocchio, which helped define the art of animation as we know it—animators have studied and used video reference. The main difference is that today it's much easier and more accessible for us to do that.
Reference is something extremely important for animators to get inspiration from and understand the essence, physics, and motivation behind movements. From video reference you can get good visual ideas to apply to your animations, especially for acting subtleties, secondary actions and timing.