The DCF valuation model considers the present value of future cash flows of the business to be the driver of value. Could there be more that adds value to the business or company?
You discount the operating cash flows to arrive at the value of operating assets in a DCF valuation. If you stopped there, you may not be including other assets such as excess cash and marketable securities. You could also have missed out other assets such as investments in other companies, minority interest, etc. Other assets that do not feature in the operating cash flows are also not valued in the DCF valuation. These assets must be valued separately and added to the DCF value to arrive at the total value of the company.