What exactly does currency import do and how does it impact on invoices and reports?

What exactly does currency import do and how does it impact on invoices and reports?

Hello,
I just noticed Zoho Invoice allows to import historical currencies values from CSV as well as adding them from the interface.
I think this is a very useful feature but I have a few questions:

1) After I import records, how will this affect my past invoices? Will prices and amounts of invoices matching date and currency code of an imported record be re-calculated according to the imported exchange rates? (My hope is that it doesn't affect amounts of past invoices at all) 

2) Will my report figures (e.g.: amount of total sales in the base currency) reflect the imported exchange rates?
(My hope here is that the import does affect the reports)

3) How are invoices matched with a given exchange rate? Will the system match each invoice with an exchange rate record only if they have the same date? Or will the invoice be matched with the closest past exchange rate record?

Thanks in advance