People naturally and willingly follow leaders due to their charisma and personality traits, whereas a manager is obeyed due to the formal authority vested in him/her. As a result, people tend to be more loyal towards leaders rather than managers.
Leadership is one of the several facets of management. Often the same people play wear different hats – both leader and manager – at different points in time. Although not essential, it certainly helps a manager if he/she is also a good leader. Conversely, leaders do well if they have some degree of management skills because it helps them envision the implementation of their strategic vision.
Self-motivated groups may not need a leader and may find leaders dominating. Alternatively, small teams may find a natural leader emerge based on his/her specialized skills. But this leader may be subordinate to the team manager in the organizational hierarchy, which may lead to conflicts.