Apply suggestions from code review

Co-Authored-By: pzuraq <[email protected]>

README.md

@@ -163,11 +163,11 @@ let app = new EmberApp(defaults, {
 #### External Helpers
 
 Babel often includes helper functions to handle some of the more complex logic
-in codemods. These functions are inlined by default, so they are duplicated in
-every file that they are used in, which adds some extra weight to final builds.
+in codemods. These functions are inlined at each location of use by default, so they are duplicated many times across an application.
+Understandably, this adds some extra weight to final builds, scaling up in proportion to use of the related language features (decorators, for...of loops, object or array spread operator, etc...).
 
-Enabling `includeExternalHelpers` will cause Babel to import these helpers from
-a shared module, reducing app size overall. This option is available _only_ to
+Enabling `includeExternalHelpers` will cause Babel to create a shared module for these helpers
+and import them at each call site, reducing the download/parse cost of these language features significantly. This option is available _only_ to
 the root application, because it is a global configuration value. There must be
 one agreed upon Babel version to generate helpers, and if any addon opts into
 generating helpers then they must be included and synced with any other addons