Sorry I meant by the service you're signing into, any of their 3rd party trackers, or in case of a data breach. This sets it apart from e.g. gmail's username+se

Sorry I meant by the service you're signing into, any of their 3rd party trackers, or in case of a data breach. This sets it apart from e.g. gmail's username+servicename@gmail.com, or a wildcard on a private domainname which only you ever use.