Investing cash flow shows cash spent on or received from long-lived assets, meaning purchases of buildings and equipment, acquisitions of other companies, and purchases or sales of investments like bonds. For most operating businesses this section is negative, and negative is normal here, since a business must keep spending on its equipment and its future.
What matters is where the money went. Steady spending on equipment that supports growing revenue is healthy. Constant large outflows for buying other companies deserve the scrutiny described in the goodwill entry. A large positive number also deserves a look, since it usually means assets were sold, which can be smart housekeeping or a struggling business raising cash by selling its assets.