I think we have all heard someone say, "I don't go to work to make friends." It's good to have boundaries between your personal life and work life. Establishing these confines is often cited as a great key to success. If you are a leader and you focus on your strength, savvy and skills, but forget to connect with the people you are leading, you may be headed for failure. There have been many strong and efficient leaders who with one slip, fell fast because no one would lend a hand when the going got tough.
Harvard Business Review explained the impacts of a leader who only focuses on competence and the implications this can have in the article, Connect Then Lead. If people remove the human aspect from their work environment and only concentrate on the task, they will lose those around them. This will also foster an "every employee for his or herself" mentality that could damage the overall productivity of the team.
We are all human and we evaluate each other based on interpersonal traits. Showing warmth to others will help build trust. It will also make people more open to you and they will truly listen when you talk. Trust is the key to teamwork and can go a long way when you need cooperation to succeed.
An effective leader has usually found the balance between the emotional and the competency sides of the equation. If you are a fierce leader, you likely have a team of people who avoid contact with you, which will impact your ability to succeed. But if you are approachable and connected to your team, then you will have the collective strength to do great things.