The intention is to charge duty on the 'transaction value' prevailing at the place from where the goods are sold. Such place is called 'place of removal'. It can be the factory gate or a depot etc.
The transaction value shall be the price for delivery at the time and place of removal. Thus, where the customer takes delivery at manufacturer's depot, the price prevailing at the depot would be the transaction value. If however, the delivery is to be given at some other place (though the sale is taking place from depot), the valuation rules provide a mechanism to work out the price at the depot (by excluding cost of delivery from depot to the actual place of delivery).
Thus, where the actual delivery is not at the place of removal, the transaction value is rejected; value is then determined under the valuation rules. The endeavour of the valuation rule is to determine the deemed transaction value - had the delivery been at the place of removal.