Impairments hit intangible-assets, goodwill, property-plant-and-equipment and inventory. The cash went out years ago, so nothing leaves the business now, but net-income and shareholders-equity both drop.
A large goodwill impairment is management admitting an acquisition did not work. It is backward-looking information, yet it often confirms what the share price implied long before.
Example: Northwind wrote $180M of goodwill onto the books from the battery acquisition. Three years later that unit's forecasts are halved and $95M is impaired. Net income swings to a loss, equity falls $95M, and operating cash flow is unchanged.
Related: one-time-charge