Once again Blizzard is hosting BlizzCon, the eighth time the company has held this convention for its most devoted fans. The audience is immense, with more than 20,000 people attending in person, with millions more expected to tune in to the more than 50 broadcast streams in 14 languages being provided by Blizzard’s wall-to-wall coverage.

The convention includes not only world final competitions in Hearthstone, StarCraft II, World of Warcraft Arena, and Heroes of the Storm, but it’s also packed with seminars, cosplayers, many new game features to try out at the show – and even a new game. Cosplayers stalk the halls, there’s a costume contest and a talent contest, and to cap it all off there’s a concert by Metallica to look forward to at the climax of the show. Oh, yes, and there’s plenty of news to set the fan’s hearts afire with anticipation and excitement.

BlizzCon is a marketing tour-de-force for Blizzard, providing value to the company on multiple levels. Before getting into that analysis, though, Blizzard’s news (announced during the opening ceremony) is quite consequential and deserves discussion on its own.

As expected, there’s more news about Blizzard’s existing games as well as announced games that are in development. All of the major World of Warcraft news coming up is already known with the release of the massive Warlords of Draenor expansion arriving shortly. Still, Blizzard CEO Mike Morhaime did announce that a charity pet will be put on sale inside World of Warcraft this December to benefit the RED Cross in Ebola relief efforts. The Warcraft movie, heading to theaters in 2016, also got a lot of attention.

Hearthstone‘s first expansion was announced as Goblins Vs. Gnomes, launching in December, along with the arrival of Hearthstone on Android tablets. Starcraft II gets a new stand-alone expansion with StarCraft II: Legacy of the Void, with a new multiplayer mode that lets two players control a single base. While Heroes of the Storm is still in alpha, the closed beta was announced for January, and the game is getting The Lost Vikings as part of the array of heroes.

The biggest news, though, was the unveiling of Overwatch, a new multi-player team battle game which many observers compared to Team Fortress. The introduction including an impressive cinematic reminiscent of Pixar films, and a healthy chunk of gameplay showing the game in action.

The advanced state of Overwatch may have puzzled some people, but it’s not surprising when you realize that much of it was salvaged from the massive Titan development project that was canceled some time ago. That game, a multi-year development effort that is rumored to have cost well over $100 million, was apparently a massive effort that included many things, and ultimately Blizzard felt it just wasn’t what they were looking for.

Judging by the enthusiastic response from the BlizzCon attendees and the Internet, though, Overwatch looks like it has plenty of audience appeal. Blizzard was careful to point out that the game would have “widespread appeal” and be very approachable, though no one from the company would address the elephant in the room – would this game be free-to-play That would seem like a distinct possibility, but we’ll ave to see how the game develops as it gets into the hands of players during the upcoming alpha and beta testing phases.

The enthusiasm generated for Overwatch (especially when it was announced that there are over 600 computers set up at BlizzCon for attendees to play the game for themselves) demonstrates very clearly the marketing value of BlizzCon. Yes, putting on an event like this is an immense effort and expense for Blizzard, which is why they haven’t made it an annual event (some years the convention just doesn’t make an appearance).

The utility of BlizzCon, even despite the cost and effort required, shows clearly the importance of audience in this era of the game industry. Hearthstone is certainly a good game, but if it didn’t have a connection to the vast and enthusiastic Warcraft audience it world certainly be much, much smaller. This show is a terrific way to keep fans engaged in the company’s brands, and to get them enthused for new brands like Overwatch. More than that, while Blizzard may or may not make money on the event, it does sell a lot of tickets to help defray the costs. Not to mention DirecTV is a sponsor, and no doubt contributing to the event. How often can you say that about marketing expenses

BlizzCon shows the value of providing content to your audience, especially when you have games that are worthy of such engagement. Now, it would make sense for King Digital to have a Candy Crush convention – the company’s products have a thin coating of content over the chewy gameplay center, and those games are not something that create fans devoted in the same way as World of Warcraft fans.

Activision has held Call of Duty conventions, which are similar but don’t have the depth or the breadth that BlizzCon does. Blizzard has a range of titles with dedicated fans and rich backgrounds, and there are few companies that can boast that. Still, some games have deep followings that might be interested in a virtual convention, or other sorts of events dedicated to fans of the game. Certainly something like The Elder Scrolls universe has the right kind of following for this.

Marketers should be taking notes about how Blizzard is creating all kinds of marketing materials around BlizzCon. The benefits don’t stop here, as fans will be watching videos created at this event for months ahead, endless articles will be written, and generally this is creating a tremendous amount of engagement for Blizzard. If you’ve got a game that has potential for deep content, BlizzCon is a master class in marketing.