It is not about anonymity, but division of identity. On Xbox live or psn, you may not want to be Derek Ross, might be bigrossman or w/e. But you may want to be discoverable and verified as both, using the same npub.
Discussion
My goal is to enable more use cases and adoption.
Basically it would you rather the user be able to use both your service to register and my service to register rather than have to pick one because they both offer different things to the user and with seamless integration via aliases they can pick which one is displayed as their primary identify action on most based portals