Sets are am amazing way of looking at slice of your data that is created dynamically.
Let’s take an example, what if I want to look at all the products being purchased by Top10 customer by Revenue. Now, this list is a list of 10 customers. But, the important thing is that this list needs to be dynamic. In other words, if my Top 10 customers change, I want to see the list of products based on a new Top 10. That’s when you can create a set. In this example, the Set will be created on the “Customer” dimension and it will have the condition of Top X in the set (similar to below)
If you read more documentation about Sets, you will realize that you can create all sorts of conditions to create a Set. That’s all I need for you to know. If you create complex calculations to create a set, the more complex your overall Data query will become and may cause performance issues.
Not, that it will, but again, many analytical expressions that you have the power to use (in Tableau) are very powerful expressions and I would hate for your to NOT use them. But, I do want you to use them where it makes sense. So, now that you have the information, use them wisely.