The LLC operating agreement specifies the working & financial relationship between the co-owners. It defines the percentages of ownership for each owner, rights and responsibilities of each member, shares of gains and losses, and a plan for the business should one owner leave.
Showing that attention was given to the organization of the LLC may make courts more likely to respect personal liability limitations. The written agreement can prevent conflict or misunderstanding regarding financial management. And, each state has default rules of operation for LLCs – create your own, so you’re not subject to default rules which may not serve you.