Main article: Why web sign-in
Web sign-in is much simpler to use and implement than previous methods of signing in with your own domain like OpenID.
Using your own domain is safer than a 3rd party email service, and simpler than email on your own domain.
See Why web sign-in for more reasons why you should use it.
See http://microformats.org/wiki/web_sign-in for a more detailed description of Web sign-in.
See also IndieAuth articles.