Users who may not want to be disturbed by random notifications from their friends on the platform, especially during moments of depression and anxiety. An (emphasis on) EASY toggle to enable and disable the ability for yourself would go a long way to improving this feature, and should be a requirement to have before the feature hits the Live branch.
As for where this could go, the most logical place to locate it would be the profile section somewhere, or within the Comfort & Safety tab as a toggle.