Hey Lucas,
There are many use cases here. A disabled user cannot sign in to an app anymore and continues to be stored in the Firebase Auth backend.
You have the ability to disable/enable a user via the admin SDK or from the firebase console.
In some cases, disabling a user is a temporary action that will allow you to enable after some action is taken unlike deleting the user.
Also unlike deleting a user, the user cannot sign up again with the same credential after being disabled, whereas, a deleted user can recreate the account after being deleted.
So I think the use case you are suggesting is a legitimate use case for disabling a user.
Bassam