Why we need creating a measure?
Why we need to create a measure here to get the total sales amount by different currencies? We have currency filter later, so when we create any sales amount bar charts and filter by a specific currency, then the charts will automatically do aggregate for us, doesn't it?
The idea is to build a measure that only gets triggered by making a selection of the currency. Here we have 30 milion of different currencies mixed up. We need to tell people that they need to make a selection of the currency which is why if no currency has been selected the user will see a message that tells them to select a currency. A user looking at 30 milion inside a bar chart is not very descriptive unless they know that they need to select a currency in order to view the data that they want to see.