Many executives and managers in a leadership role think their job is to manage teams, work, and the organization through a transition. While this is true, a manager can not see through the eyes of other employees and may need assistance getting honest and objective perspectives. After 15 years in-house focused on organizational development, I recognize that hiring a consultant costs money, but I can also tell you that it's well worth the time and energy you won't waste sifting through internal politics, deciphering employee perspectives informally or through a survey that they are afraid to answer because they don't believe it's actually anonymous.
You can get more done and be a lot more productive if you allow for an independent third-party to help you through a transition by taking stock of the current situation, identifying challenges, and working toward goals regardless of organizational norms or quirks. A consultant comes to an organization using confidentiality, trust, and they are going to give you the good, bad, and ugly since they are not concerned about retribution by providing honest insight. Nor is a consultant motivated by climbing a hierarchical ladder or a bonus at the end of the year. A consultant can help you clear the cobwebs and find out what people need, what drives them, and how to get them to buy-in to (and even lead) change. To get true insight and enhance productivity, isn't it worth the expense to gain an objective perspective from a person who will work hard so that you can keep things moving forward?