Right now we tag most fields as stored in Elasticsearch but on further reading we should really only tag the fields that we need for prefix searching. The reason for this is that during full text search we actually would load most of the _source document any way when you measure by size by virtue of highlighting the text. Once you load most of the _source you may as well get everything from it.
In other words, setting a field to stored only speeds up queries that *don't* highlight or return the text but *do* highlight or return the stored field. It actually slows down things that *do* highlight the text because it involves multiple loads. Also, it takes up extra disk space.