One of the first things you have to deal with when creating web applications is data persistence. You have data, and it needs to live somewhere, and you want to make it easy to find, edit, and delete. There are three main options: 1) store your data in simple files on the server; 2) store your objects using some kind of object database such as ZODB, Druis, or Axiom; or 3) use a relational database. By far, the most popular of these three to date is using a relational database. And so, TurboGears includes SQLObject to make storing your data in a relational database as easy as possible.
Nothing in TurboGears precludes using file-based storage, or a Python-based object database to store your data. For the vast majority of cases, however, using an object relational mapper (ORM) such as SQLObject makes using a relational database the easiest and best solution for your TurboGears application.