In the most pragmatic of ways, I would initially suggest that the effective leader understands the needs for "different tools for different jobs." In a varied workforce that is comprised of individuals with different skill sets, I think that the effective leader understands that there are different approaches with work with different people.
The workforce is not static or homogeneous. Rather, it is fluid, dynamic, and intricate. The effective leader understands which approach works best with which person and wears "different hats" in order to ensure efficiency and success is the key element.
This is not to say that the effective leader is multiple people. Their vision should be intact and their goals should still pushing them to achieve the job they wish to achieve.
However, the reality is that the leader who understands how to best work with their employees understands that motivation is knowing what buttons to push when and how to push them. This requires a keen insight into the manager and the workforce with which the manager must interact.
It is here where I think that the understanding of which leadership styles work with which team members becomes of vital importance in order to ensure efficiency and success for the organization, in general.