From a purely theoretical point of view, you are hopefully convinced that utilizing the Drupal source code to help you create a website is an excellent choice. Of course, knowing this doesn't help you discover exactly what can be done with it from a practical point of view. You still need to know what types of sites are commonly created with Drupal. As mentioned earlier, any enterprise that requires a fair amount of working with content is a likely candidate for Drupal.
Due to its extensibility and flexibility, you are really not very limited in what you decide to do with Drupal. The following list shows the most common uses at present and comes from the case studies page ( http://drupal.org/cases) on the Drupal site:
Community Portal Sites (The term portal refers to a site that is supposed to be an Internet user's point of entry on to the Web): If you want a news website where the stories are provided by the audience, Drupal suits your needs well. Incoming stories are automatically voted upon by the audience and the best stories bubble up to the home page. Bad stories and comments are automatically hidden after enough negative votes.
Personal Websites: Drupal is great for the user who just wants a personal website where (s)he can keep a weblog, publish some photos, and maybe keep an organized collection of links.
Aficionado Sites: Drupal flourishes when it powers a portal website where one person shares their expertise and enthusiasm for a topic.
Intranet/Corporate Websites: Companies maintain their internal and external websites in Drupal. Drupal works well here because of its flexible permissions system, and its easy web-based publishing. You no longer have to wait for a webmaster to give word about your latest project.
Resource Directories: If you want a central directory for a given topic, Drupal is the right tool for you. Users can register and suggest new resources while editors can screen their submissions.
International Sites: When you begin using Drupal, you join a large international community of users and developers. Thanks to the localization features within Drupal, there are many Drupal sites implemented in a wide range of languages.
Education: Drupal can be used for creating dynamic learning communities to supplement the face-to-face classroom or as a platform for distance education classes. Academic professional organizations benefit from its interactive features and the ability to provide public content, member-only resources, and member subscription management.
Art, Music, and Multimedia: When it comes to community art sites, Drupal is a great match. No other platform provides the rock-solid foundation that is needed to make multimedia rich websites that allow users to share, distribute, and discuss their work with others. As time goes on, Drupal will only develop stronger support for audio, video, images, and playlist content for use in multimedia applications.
I guess I should make it clear that while you can use Drupal for a great number of things, you should perhaps limit what you use it for to those things that complement its design—like those mentioned in the previous list. If you want to retail a large number of goods from your community website, then you might wish to consider using something like osCommerce that is designed specifically for that purpose even though it is possible to retail products off your Drupal site using a contributed module.