Once I asked a fellow businessman, "How many clients do you have?" he replied, “600 to 700 clients!!”, when I asked "How client count can be approximate number?, Why not a definite count as reply?" He was not able to answer. This is because he does not maintain any database of the clients or customers.
When you are in business, you should have the complete database of your clients with all possible information including and not specific to "when they do Business with you, how much business they have given so far, How many clients and customers they referred? Through what source you got the client? When was the last time you contacted the client? If you can have information like this about all your clients you will enjoy the benefit of the repeat orders and more referrals from your clients.
In Business one should focus on profits, where the profit comes from and how it comes. Profit comes from every sale, profit comes after all expenditure and costs, acquiring a client has a cost and by saving on the client acquiring cost, you increase your profits.
Maintaining client database not only helps to retain the client and get few more referrals from them but whenever new product and services are introduced you can just go through the database and find instant prospects who will buy your new product and service.
There are so many ways and approaches to maintain the client database, you can use online google spreadsheet, use an excel file, even maintaining it on an index notebook. But maintaining a client database is a must and it makes you as better business person in many aspects.