Threading and locking are very important for multiple-tier sites and two-tier sites that have many contributors. They prevent two database calls from bumping into each other, so to speak, by giving editorial control to only a single transaction at a time.
An example that clearly illustrates the value of threading and locking is a Web site that sells tickets to popular rock concerts (assigned rather than “festival” seating). Obviously, you would not want two people to be able to purchase the same seat at the same event due to a database error. The database needs some way to recognize unique requests and let only one user (or thread) make changes at any given moment, while others are locked out until the first transaction is complete.
Unless you’re sure your project (a Web log, for instance) will have only one user at a time, be careful of committing to a nonthreaded database.