- Everyone can see what you read. This is a good thing, as one should always talk about the books one enjoys. Now, if you are ashamed of what you read--afraid your friends will find out--maybe it's time to get new friends.
- Energy efficiency. What better way to insulate a house than by packing the walls with bookshelves?
- Happiness. Every time you glance at your books, you'll be reminded of the lovely stories you read therein. This is good for the soul.
- One of the best ways of storing books. Unless you're archiving rare or damaged books, bookshelves are one of the best ways of storing books long term.
Books should stand upright, never leaning. If you can't stand books upright, stacking horizontally is the second best way. Never rest a book long-term on its spine or (heaven forfend) fore edge. Also, keep out of sunlight, away from humidity and keep the dust and insects away. Silverfish are a bane to books, as is mold and mildew. The airflow is good on a shelf. Books need airflow or they get musty.
Her Grace has a house full of bookshelves, and is planning on building more.