IMO, current description lacks a good example.
Quoting Chris @Naros Cranford that provided a good one:
Lets say you have some tables that have lots of rows in them but you use a soft delete column and you're only interested in rows during the snapshot where the record isn't soft deleted, then you would use:
"snapshot.select.statement.overrides.dbo.my_large_table_with_soft_deletes": "select * from [dbo].[my_large_table_with_soft_deletes] where delete_flag = 0 order by id desc"
For this large table, only records where delete_flag = 0will be emitted as snaphot / read records.