Earlier, Pierre de Fermat had introduced the ideas that rays of light, in optical conditions such as refraction and reflection, followed a principle of least time: see Fermat's principle.
The principle of least action led to the development of the Lagrangian and Hamiltonian formulations of classical mechanics. Although they are at first more difficult to grasp, they have the advantage that their world-view is more transferable to the frameworks of relativistic and quantum-mechanical physics than that of Newton's laws.
This has caused some people to think that this principle is a "deep" principle of physics.