The employer needs to know the complete address of the employee for a number of reasons. One is for payroll purposes. Setting up an account for a person requires him to provide his address. Another reason is that if something wrong happens, they would know where to locate him or his family. The company also needs an employee's address so that they can be certain of his identity. And another reason would be for mailing of anything necessary purposes.
Letters for every situation that may arise regarding your businesses cash flows, such as an overdue account letter can quickly be put together and sent out if you have a standard letter ready. You will also need forms and letters to assist with your customer relationships. You should have a standard 'client details' form ready for each customer's details and preferences to be filed. You also need customer feedback surveys and a series of letters welcoming new customers and dealing with various other complaints and issues.