Use Elasticsearch when:

• You want to do a lot of text based searches.
• You want to analyse huge amounts of data which are non-relational. For example, analyse varied logs from applications which are non-relational and require text based searching to make sense of it.
• You are looking for lightning fast query results, especially if you are looking for text based search for dealing with autocompletion in your application.
• You are looking for a schema-less data store (explicitly it is really good to store JSON documents).