[DOCS] Add performance info for runtime fields (#74454)

* [DOCS] Add performance info for runtime fields

* Add script-based sorting and clarify performance

* Changing title to Incentives and reworking the intro

docs/reference/mapping/runtime.asciidoc

@@ -42,6 +42,38 @@ front, and can use runtime fields to amend the mapping at any time. Using
 runtime fields allows for a smaller index and faster ingest time, which
 combined use less resources and reduce your operating costs.
 
+[discrete]
+[[runtime-incentives]]
+=== Incentives
+Runtime fields can replace many of the ways you can use scripting with the
+`_search` API. How you use a runtime field is impacted by the number of
+documents that the included script runs against. For example, if you're using
+the `fields` parameter on the `_search` API to 
+<<runtime-retrieving-fields,retrieve the values of a runtime field>>, the script
+returns only the top hits just like script fields do.
+
+You can use <<script-fields,script fields>> to access values in `_source` and
+return calculated values based on a script valuation. Runtime fields have these
+same capabilities, but provide greater flexibility because you can query and
+aggregate on runtime fields in a search request. Script fields can only fetch
+values.
+
+Similarly, you could write a <<query-dsl-script-query,script query>> that
+filters documents in a search request based on a script. Runtime fields provide
+a very similar feature that is more flexible. You write a script to create
+field values and they are available everywhere, such as
+<<search-fields,`fields`>>, <<query-dsl, all queries>>, and
+<<search-aggregations, aggregations>>.
+
+You can also use scripts to <<script-based-sorting,sort search results>>, but
+that same script works exactly the same in a runtime field.
+
+If you move a script from any of these sections in a search request to a
+runtime field that is retrieving values from the same number of documents, the
+performance should be about the same. The performance for these features is
+largely dependent upon the calculations that the included script is running and
+how many documents the script runs against. 
+
 [discrete]
 [[runtime-compromises]]
 === Compromises

docs/reference/search/search-your-data/sort-search-results.asciidoc

@@ -591,6 +591,7 @@ The final distance for a document will then be `min`/`max`/`avg` (defined via `m
 
 
 [discrete]
+[[script-based-sorting]]
 === Script Based Sorting
 
 Allow to sort based on custom scripts, here is an example: