Why should we use webapi keys

Why should we generate api keys for domains to use web api when we have the referrer开发者_运维技巧 to check the source of the request?

The value of HTTP_REFERER can easily be faked. If you want to verify that somebody (or some website) is really entitled to access a service, you have to involve some sort of authentication, which generally means an API key (or for people, a username/password).

Some browsers don't send REFERER headers.