But as you advance in your dancing, it becomes more and more important to understand what muscle groups are working and how, and which muscle groups are relaxed and not working!
Usually when you see someone look like they are working too hard, they are probably applying muscular pressure in a "wrong" muscle group (and their bodies are having to deal with tension that is hindering movement rather then helping), or they are using the muscle groups to "hold" or "clench".....It is "effortless" when my body has learned how to perform the actions well and has the stamina to maintain that level of work, but the amount of energy required is still the same (rather intense and focused).