Pros

The ability to have virtually unlimited speech in online games has created a unique atmosphere that would be impossible without anonymity or if censorship was implemented.

Gaming/Social Atmosphere

Speech in online games adds an interactive aspect to games and provides the ability to participate in a collective gaming community by connecting users to one another.  Players are able to communicate directly and instantaneously with each other while enjoying the game. This has led to a complete change in how we view the video game experience. Where it was once one versus the computer, it is now teams of players versus others from around the world.

Ability to implement interactive strategies

Many online games include multiplayer operations and the ability to speak. With the inclusion of speech and the pre-game/post-game lobbies, players are able to develop better team cooperation and strategize plays to gain an advantage. This ability has led to the massive expansion of gaming leagues and the creation of the Major League Gaming association.

Enjoyment 

The mass inclusion of speech has added another layer of connectivity between players from when communication was purely visible with text or non-existent. Games have become much more social and therefore more enjoyable. In addition, much like in any competitive platform, trash talk is common.  Trash talk serves to make the game interesting and enhances the competitive nature of gaming.