Before reviewing the positive and negative aspects of hiring a professional business plan writer, you should consider the purpose of your business plan. If you are writing a business plan for your own
There are two schools of thought on hiring someone to write a business plan for you, which is the basis for the pros and cons listed here. In addition, to help you with your decision, read Professional Help in Writing Your Business Plan.
Pros:
Will take an objective approach and not be guided by enthusiasm Can save you hundreds of hours of time and research Will know what needs to be included and can add valuable ideas Has experience at writing in a manner with which investors are familiar Will get it done in a set time frame and not extend the planning and writing process (as you might)