It is very common to have a lot of different types in several indices. Because Elasticsearch makes it possible to search in many indices, you should filter for common fields at the same time.
In the real world, these fields are not always called in the same way in all mappings (generally because they are derived from different entities), it's very common to have a mix of added_date, timestamp, @timestamp, and date_add fields that are referring to the same date concept.
The alias fields allow you to define an alias name to be resolved, as well as a query time to simplify the call of all fields with the same meaning.
