GSTR-1: what goes out
The outward supplies summary comes out grouped the way the return needs it — B2B invoices with each buyer's GSTIN separated from B2C, credit and debit notes listed, an HSN-wise summary built from the item records, and tax broken down by rate. The classification happens once, when the item is created, instead of once a month across four hundred bills — which is the whole reason a mixed-slab material shop can close a month in minutes rather than days. Your accountant uploads or keys from that summary rather than reading invoices.
GSTR-3B and the input side
The 3B summary needs outward tax and input tax together, which is where shops that only record sales get stuck. Purchases entered properly capture the input GST on every supplier invoice, so both halves of the return exist in one place. It also means you can see, before filing, whether your input credit looks like what you expected — a large gap usually means purchase bills that never got entered, and finding that before the return is filed is considerably better than after.
Reconciling with what suppliers reported
Input credit is only available for invoices your supplier actually reported, which is why the 2B reconciliation exists. With every purchase recorded against a named supplier with its invoice number and date, comparing your records against the portal is a matter of matching two lists rather than reconstructing one of them. The differences that show up are usually a bill you never received or a supplier who has not filed, and both are worth a phone call while the quarter is still open.
Keeping it clean through the year
Most filing pain is created eleven months earlier by small habits: bills raised outside the software, HSN codes left blank, cash sales without a party, purchase invoices in a pile on the desk. None of them hurt on the day. All of them surface at return time or, worse, at scrutiny. The advantage of doing every bill and every purchase in one system is not the report at the end — it is that there is nothing left to reconstruct.
What the software cannot do for you
It will not file the return and it will not replace your CA, and any product claiming otherwise is worth a second look. What it removes is the part that actually takes the three days: rebuilding a month of figures from a bill book because nothing was classified when it was written. The return itself still needs a person who knows your business to look at it before it goes.