While this is fine for some scenarios where you want to stamp and lock the FX rate on the record it is not appropriate in others. A typical scenario is when you have multi currency opportunities and you want to report on these using the latest exchange rate. If you use the base amount then you will get the base currency value at the time the record was saved. Prior to the release of Dynamics CRM 2015 using the current exchange rate was difficult to achieve without custom code.
The introduction of calculated fields in Dynamics CRM 2015 will allow us to calculate the estimated revenue of an opportunity in the base currency using the latest exchange rate. This technique can also be used for many other scenarios where you want to lookup the latest price or rate to calculate the latest value of a record.
Follow these steps to create a calculated field that will show the opportunities estimated value using the latest exchange rate. Create a new field on the opportunity entity of data type decimal and field type set to calculated.
Now goto Settings-> Business Management -> Currencies and change the currency exchange rate.
Refresh the view and you will see the new rate is being used in the calculated field and you can see the difference between it and the base estimated revenue.
The benefit of using calculated field is that they are calculated when the records are retrieved so all your views, reports and dashboards will use the latest exchange rate without the need for any custom development.