Question

What is the Auto-Close option when creating a new database in SQL Server 2008?

EDIT: and how do you decide whether to turn it on or off?

Answer 1

From MSDN:

If True, the database is closed, and its resources are freed when no user connection accesses the database. If False (default), the server maintains the database in an open and ready state regardless of user activity..

Edit to answer edited in question: It all depends on whether the server needs the extra memory, and if the time cost to open and close the database is worth the extra memory gained. If you are unsure, then false is probably the way to go.