Google's (GOOGL  ) ad machine is integral to the revenue generation of many small and big businesses, to the extent that not having it impacts profitability significantly.

For instance, Nexstar Media Group Inc., the largest local news company in the U.S., conducted a test to see what the effects of not using Google's services on its websites would be. What ensued was chaos, with the firm's ad sales dropping significantly: "That's a huge revenue hit," said Tony Katsur, senior vice president at Nexstar.

Because of this immense influence that Google has over the various companies it provides tech to, The U.S. Justice Department is investigating whether the ad giant is abusing its power.

This wary disposition was established back in 2008, when Google acquired DoubleClick, a huge ad-tech company that endowed it with the necessary technical apparatus to gain significant market power. In fact, regulators who approved the $3.1 billion deal back then itself also said they would take swift action if this power became too great and unchecked later.

That said, Google is not the only ad player in town. Amazon (AMZN  ) also has a significant ad revenue machine that is growing, with CFO Brian Olsavsky reporting that "advertising grew at a rate higher than that 45%" last quarter.

In fact, Amazon's main ad sales come from search results on its marketplace. When a user enters a relevant search request, Amazon displays sponsored brands and product listings from advertisers that bid on the keywords that a customer types into the search bar. In this way, Amazon thus makes it more likely that consumers will actually purchase the product, by establishing associations between those keywords and that particular product.

Forbes reports that Google's 3 divisions , which include Google Advertising Revenues, Google Other Revenues and Other Bets Revenues, are expected to contribute $142.4 billion (83.3%), $27.9 billion (16.3%) and $0.7 billion (0.4%) respectively to the company's 2019 revenue of $171 billion.