Broader knowledge, more management tools and techniques
A management consultant provide different management consulting services to clients, and thus possess broad knowledge, management tools in different aspects. An experienced management consultant serves many different companies, he/she can usually apply good practice in the industry or a more advanced management techniques to his/her clients.

Hiring Management Consultant vs. Staff
When a company has good human resources management, and staff turnover rate is low, the company can tend to hire staff instead of consultant. However, if the turnover rate is reletively high, hiring a consultant is the best solution.
A management consultant can serve the company in long run, and thus no need to worry about turnover problem. Some management consultants focus on providing advices only; however, some management consultants, like HKMC, can directly help clients solve their problems and make things done, similar as part-time staff or sub-contractors.

Is management consulting extra cost?
No. By contrast, it is a cost-effective solution. It is true that sometimes what a management consultant does can be done by internal staff, however, costing much more resources in a longer duration. Especially when relevant job/project is new to internal staff, relevant staff usually have to spend more time to do it.