"Best practice" these days is that mailing lists must not only be explicitly signed up for ("opt-in"), but must also be confirmed via email from the address subscribed. This prevents people being signed up for lists they don't want as a "prank".
Uncle Hugo has three mailing lists. This form allows people to subscribe or unsubscribe from any of them. People can get notification when a new newsletter is posted to the site, when there's an SF-related announcement from Uncle Hugo's, and when there's a mystery-related announcement from Uncle Edgar's (it often happens that author appearances are scheduled too late to have appeared in the newsletter, which only comes out quarterly).