Publishing publicly subscriptions of a user has pricacy implications: those public subscriptions may be used by someone to get a user interests or to know they network of contacts.
It may be used by bad actors for many reasons like advertising, or it may even be life threating in some countries/situation as it may be used to known political opinion, religion, sexual orientation, etc. A client SHOULD make the subscription public only if there is no doubt that this is what the user wants, by using an opt-in system, and SHOULD display a well visible warning about the consequences of making a subscription public.
+By having subscription public, an entity JID can be checked or harvested by doing a request on the public subscriptions node. A client SHOULD display a warning clearly indicating that making subscriptions public makes its JID discoverable.
+For the same reason, a server SHOULD respond identically to a pubsub request to public subscriptions node if the user doesn't exist or if they exist but they don't have any public subscriptions.