1. DCLGEN is an utility/tool of IBM for generating equivalent declaration for table in for using in COBOL,Pl/1..... languages
2. It's not compulsory, if u know declaration of table in languages then we no need to use DCLGEN.
I too agree with the above points. Though it is optional, please make use ot the utility to get the language (eg, COBOL) equivalent host variable declaration generated, instead of commiting mistakes while defining them in the program.
Declgen will provide the mapping of datatypes of table fields with the language you are using.
Let me know if U still have any queries.