Dual Axis allows you to compare measures, and this is useful when you want to compare two measures that have different scales.
Considering the same example used in the above question, first create a visualization with sales over time and profit over time. To create a dual-axis, right-click on the second pill of the measures and select Dual Axis.
Observe that sales and profit do not share the same axis, and profit is much higher towards the end.
The difference between a blended axis and a dual-axis chart is that the blended axis uses the same scale, while a dual-axis could have two different scales and two marks cards.
Scenario: We want to show Sales by year and Profit Ratio by year in the same view.
We create a visualization of sales over time and profit ratio over time. Observe that sales and profit ratio can’t use the same scale as the profit ratio is in percentage. As we want the two parameters in the same area, we right-click on Profit Ratio and select Dual Axis.