Here are some of the less obvious benefits of having a library card:
1. Access to ebooks, music and other downloadables: The libraries of today aren't just about traditional paper books. They most often offer access to ebooks and audiobooks. Many libraries even offer downloadable free and legal music through services such as Freegal.
2. Databases for research: Libraries subscribe to databases for all different purposes. Some are geared towards children, others towards adults and/or teens. These databases provide library card holders access to the full text of articles from books, magazines, newspapers, etc. They are easy to search and a lot more reliable than stuff found freely available on the internet.
3. Passes to museums, parks and area attractions: Libraries participate in programs such as the Michigan Activity Pass program, which allows you to check out passes that are good for admission and/or discounts at local attractions. In my neck of the woods we also have the MI Big Green Gym program, which allows check out of passes to local parks.
4. Fun and useful programming for all ages: Some libraries require a card to attend all the great programs going on at the library. Typical programs include storytimes, book groups, and computer classes. There is usually something worth attending for every age and/or life stage. Not having a library card can mean missing out.
5. The sheer power of knowing all that is available to you. Library cards give you access to knowledge, which is the greatest power of all.
Any advantages I've missed? Feel free to share in the comments :)