Leaders are responsible for challenging their direct reports to personally grow and providing resources for their development. Leaders are not responsible for teaching, just the inspiration.
On-going personal development can be of the mind (intellectual), body (physical), heart (relationships), or spirit (values). Too often development is just focused on the intellectual (mind). There is nothing wrong with encouraging direct reports to grow in all parts of life.
Taking an aerobics class (physical); spending more time with the family (relationships); or attending a spiritual retreat (values) are all effective personal development activities that can make direct reports more productive.
The leader's job is to empower their direct reports to develop. Their continued growth and development - in all aspects of their life - will lead to everyone's success.