Can anyone help in understanding more about ‘SET statement’ in KQL?

I referred the documentation in the link https://learn.microsoft.com/en-us/azure/data-explorer/kusto/query/set-statement?pivots=azuredataexplorer.

But I could not figure out on what situations should we use this, the examples provided here is not enough. Can someone provide more information or any realistic examples about when and where to use SET statement in KQL.