UDT's or User Defined Data types are extremely useful in the Logix platforms.  Keep in mind when creating them to gourp similar data types together to achieve the best memory optimization.  In other words group all your bits, integers, floats, etc together when designing the UDT.  The problem with designing a type that alternates between a DINT and a Binary data type is that the processor can not just allocate a single bit adjacent to another data type.  Instead one bit will be used out of a 32 bits and the other 31 bits will be wasted memory.  However if you grouped 20 bits together in your UDT then some memory would be wasted, but not as much as if the bits were scattered throughout the UDT.