Manager roles concerning routine management, focus to the performance and efficiency of resources.
Leader roles concerning changing of innovation in the performance, effectiveness and can persuade/influence people to do.
Leadership is important for project managers because they must contact to stakeholders and good cooperate with them for successful of his/her project management. Such stakeholders consist of project teams, other project manager, functional manager, administrative support, top management, others organization, project sponsors, contractors, customers, and government agencies. Stakeholders are the variety peoples that differentiate in culture/rule/want/need which not easy to manage or persuade them.
Then project managers should learning about strategies to using leaderships. Strategies to using leaderships will difference way (not same) in different people/time/place, it belongs to situation.
The 1st thing of strategy is good relationships because humans sensitive about emotion, so project managers should built them before used because its need time to build.
The 2nd thing of strategy is trust because it is face to face contact between human, managers should do a good pattern/model about sincere, honest, decision making, flexible by seasonable, earnest, and creation; those are the tactics of leadership.
The 3rd thing of strategy is thinking about leery of the golden rule (want or need not same) so manager should care about feeling of others, empathy in coworkers or stakeholders is need for good relationship and trust, fairness feeling has level belonging to want and need of each persons. Acknowledging in differentiation of humans will help managers to find values in different humans and use its effectiveness.