Sets

Sets - are custom fields that define a subset of data based on some
conditions. Computed sets update as data is being changed.
-> Alternatively, a set can be based on specific data point in your view.
Sets are sub set of data, which are derived from either only Dimension or combination
of Dimension & Measures.
EX:
1) Right click on Region, cick on "set".
2) Click on condition  "By Field", Select the measure, define condition.(Sales>=10000)
3) Click on "OK".
4) Set has been created, it shows the list of customers whose sales are more than 10K.
EX: Combine sets
1) We can use the sets for set analysis.
Set 1 = Top 3 Customers
Set 2 = Bottom 3 Customers
2) Combination of Top 3, Bottom 3
Set 1 Union Set 2
3) Right click on Set 1 then click on "Combine Sets"
then select option "Union"
Additional Points:
1) We can use Parameters instead of Top 3 as Top N.
And We can use Parameters instead of 10k.
2) We use sets for set Analysis like Union, Intersect, Minus.