No revenue or costs from the investee appear in the investor's statements, only a single share-of-profit line. That means a company can own economically important assets that are almost invisible in its revenue and ebitda.
For valuation, strip the equity-method profit out of earnings, value the stake separately at market or book value, and add it back. This is a standard step in sum-of-the-parts.
Example: Northwind owns 30% of a distributor that earns $40M. Northwind books $12M of income and carries the stake at $105M, with none of the distributor's $600M of revenue appearing in Northwind's top line.
Related: non-controlling-interest, other-income-and-expense, net-income