Manually creating a data type lets you use all the capabilities built into the syntax of data type definitions.
You must create an data type manually if you want to use these features of data types:
Location (path)-based data typing
The ability to specify actions associated with the data type other than Open and Print
Multiple name, pattern, or content criteria for the same data type—for example, a data type based on files named *.abc or *.def
Link-based data typing