> do we need to express field type? We know it, no? What about non mapped fields?

It would really be nice to be able to not have to define the type when we know it. It caused us a lot of headaches when the Date index format was changed from a String to a Long.

> Why does ES has unit on distance sorting? How does that influence sorting?

It does not influence sorting but ES automatically include the distance in the results when you sort by distance.

We use it here: https://github.com/hibernate/hibernate-search/blob/master/elasticsearch/src/main/java/org/hibernate/search/elasticsearch/impl/ElasticsearchHSQueryImpl.java#L541 .