Transaction type defaults are used to pre-code specific transaction types for the employee, eg. account fees or transaction fees. As an administrator, you can set a default code for certain transaction types to save time for the account holder when coding their transactions.
You also have the ability to customize the behaviour of transaction types. For example, you can define the description that will appear in the Description field of the Coding tab of the Transaction Details window or, if your organization uses the Spend Wizard module, you can force users to complete a Spend Wizard for particular transaction types.