There is always a bit of controversy within the management community regarding the relationship between personality and leadership. This is especially true when discussing the selection of new leaders, because the role of personality and leadership success is hard to determine precisely as there are many factors that contribute including: experience, technical/business expertise, specific match between job requirements and the candidate, cultural fit AND personal qualities like cognition, motivation and personality.
Yet, when reviewing personality assessments with my coaching clients, I am always impressed by the interplay between one's personality and work behavior. For example, the leader who is highly extroverted, social and spontaneous will bring this to work. Yes, it is "personal". Yes, it is not the same as education, training or work history. However, these characteristics impact one's work. And there is the potential for positive or negative impacts. It may be that the extroversion aspect of the leader helps him or her engage with others and develop the strategic relationships critical to success. On the other hand, he/she may be less effective in work situations that require long periods of focus, reflection and analysis that are needed for complex decision-making.
This is just one example, and, of course, there are many others. The bottom line is this: we bring our whole selves to work. Like it or not, when we arrive at work, our personalities arrive with us. Of course, we moderate our behavior according to the context; what's appropriate at home is not necessarily appropriate at work. Nonetheless, understanding "who we are" as people will help us to be better at our jobs. It also, of course, helps us to be better at our lives.