User defined data type

CREATE TYPE [dbo].[u_ChequeNoLen] FROM [varchar](11) NOT NULL

WHY USE user defined Data Type when contains similar to defining a system data type?

1.advantage is only for development phase

* when used ud data types .. represents similar data type.

*if it is very sensative data type, developers might use the it as other data type when it requires varchar or int of specific length .. which might arrise many problem in future .