reset() can be used to reset bean properties to their default state, as needed. This method is called before the properties are repopulated by the controller.
The default implementation does nothing. In practice, the only properties that need to be reset are those which represent checkboxes on a session-scoped form. Otherwise, properties can be given initial values where the field is declared.
If the form is stored in session-scope so that values can be collected over multiple requests (a "wizard"), you must be very careful of which properties, if any, are reset. As mentioned, session-scope checkboxes must be reset to false for any page where this property is set. This is because the client does not submit a checkbox value when it is clear (false). If a session-scoped checkbox is not proactively reset, it can never be set to false.
This method is not the appropriate place to initialize form value for an "update" type page (this should be done in a setup Action). You mainly need to worry about setting checkbox values to false; most of the time you can leave this method unimplemented.