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How profitable is your business? You'll never know if you're not keeping track—which is reason enough to set up some sort of recordkeeping system.
Keeping records can be both a defensive and an offensive (in a good way) activity. It's defensive in that you have key information about your business in case you ever need it in the future—to answer a query from the IRS, to investigate a customer complaint, or to notify customers in the case of a product recall. It's offensive in that you can use this information to generate more sales, by selling additional items to your existing customer base.