You would choose to advertise on the Google Display Network if you wanted to:

Show ads on Google Shopping
Show ads to people on non-Google search sites
Show ads on Google Maps
Show ads on websites related to your business

Explanation: “Display Network only” campaigns are best if you’d like to show ads on websites and apps when your keywords are related to the sites’ content. Your ads are matched to websites or mobile apps (called placements) that include content that’s related to your business or to your customers’ interests. You can set up targeting to match your ads to the most relevant Display Network sites based on their topics, interested audiences, demographics, and more. Read more here

See all AdWords Fundamentals Questions and Answers here.