What is the need to have separate rules for place of supply in respect of B2B (supplies to registered persons) and B2C (supplies to unregistered persons) transactions?

In respect of B2B transactions, the taxes paid are taken
as credit by the recipient so such transactions are just pass
through. GST collected on B2 B supplies effectively create a
liability for the government and an asset for the recipient
of such supplies in as much as the recipient is entitled to use
the input tax credit for payment of future taxes. For B2B
transactions the location of recipient takes care in almost
all situations as further credit is to be taken by recipient.
The recipient usually further supplies to another customer.
The supply is consumed only when a B2B transaction is
further converted into B2C transaction. In respect of B2C
transactions, the supply is finally consumed and the taxes
paid actually come to the government.