Significance of Invoice Processing Currency

 Hi All,

what is the significance of selecting invoice processing currency in the project

I can understand that this is the currency in which the bill transactions are converted and checked against the agreement before converting to Invoice currency.

In our company the project currecy could be in INR or USD. And the customer Invoice currency is again INR or USD.There is no Invoice by BTC.

In this case what should I be selected as the Invoice Processing currency.

Thanks

Nandini