Sorting a measure across two dimensions was inexplicably difficult prior to Tableau 2018.2. If you tried to sort the categories by Sales for each dimension, you would see the following:

As you can see, the categories were sorted without taking the years into account (making it difficult to rank the categories in 2016 or 2018, for example). It was possible to get the desired sort with a hidden combined field or some table calculations, but everyone agrees that it was unnecessarily complicated. 

From Tableau 2018.2, if you click on the Sort button on the axis, Tableau creates a nested sort, displaying the best Category per year as follows:

If you still want to use the previous method of sorting, you can use the sorting icon in the toolbar. 

This small enhancement makes the product a lot simpler to use. The next feature is quite similar, with a simple addition having a tremendous positive impact.