Susan Beebe’s answer to Is there any point in tracking expenses in starting up a startup?
A startup is a business. As a business, you need to know how much money you are actually making in order to make effective decisions.
Additionally, you must present your company "financials" to a bank for funding; same is true for VC cash. Begin owning and operating your company as a "real" company from the start so you don't have to play catch up later to justify your financial needs. Furthermore, if you don't have a firm grasp of your operations you won't have the information YOU need to plan your company's future growth.