Different options for "Delete Instances..."

I'm all for whatever feature requests people would like, go for it! But I'm kinda wondering what the use case with this one is or if I'm misunderstanding something. I assume this is referring to the option to auto delete an instance in a DataSource when autodiscover no longer discovers it. The 30 day option is more of a grace period so if autodiscover then re-finds the instance you don't lose past data.

Regardless which option you chose, the instance still disappears immediately from the portal and can't cause alerts from my understanding. I would understand if this would keep the instance visible and alertable during the X days but I don't think it works like that. Would a use case be for an instance to reappear and kinda reset past data after 7 or 14 days? Or am I missing understanding something or don't see a potentially useful and outside-the-box use-case?