If you want to return an Observable some other code can subscribe to, but you still want to manipulate the data events in the current method, use map.
The actual user of the observable needs to subscribe(), because without subscribe() the observable won’t be executed at all. (forEach() or toArray() and probably others work as well to execute the observable instead of subscribe())
subscribe() returns a Subscription that can not be subscribed to, but it can be used to cancel the subscription.
map() returns an Observable which can be subscribed to.