Do you recommend passing default locale's messages to an intl object?

[BlueCutOfficial]

Let's assume my default locale is en-us. If I use this in production:

let intl = createIntl({
  locale: 'en-us',
  defaultLocale: 'en-us',
}, cache)

then formatjs fallbacks on the default locale after executing a couple of instructions. Does this approach has downsides compare to compiling the en-us.json file and defining the messages field like for any other language? or is it even better?