One of the Growth team's current area of focus is campaigns - inviting new audiences to become edithors, via emails, social media ads, GLAM editing events etc. This involves hand-crafted messaging that only participants of the given campaign will see. These messages are usually needed in a few languages, but there is no point in translating them to languages in which the campaign is not exposed.
Using the standard translation pipeline for such messages will expose translators to messages the translation of which would be a waste of their time, adds noise to message lists and stats, and risks the overwriting of messages by translators who don't fully understand the context. They could be configured as optional or not-to-be-translated messages on the Translatewiki side, but that adds a maintenance and communication burden, as a new set messages is usually needed for every campaign.
A possible solution to this problem would be the creation of a new campaigns or notranslate message directory which is not registered with Translatewiki, so all message keys in this directory are ignored on that side.