If you file your GSTR1 data quarterly, you are classified as a quarterly filer. As a quarterly filer,
you need to generate your GSTR1 on a quarterly basis. You only need to generate the Invoice Furnishing Facility
(IFF) during the first and second months of the quarter. IFF only includes B2B transactions and credit/debit notes
issued to registered persons. In the third month, you must generate GSTR1. GSTR1 will contain
all the data of that quarter, except B2B transactions of the first and second months.
So that's why you have to use Skip option while Generating GSTR1.