One of the essential tools in our business/development process is Campfire, a group chat application. Every developer is always logged in whenever they are working, and it is the primary channel we use for intra-team communication. It's a place where we share news, ask questions, get notified about broken builds, solicit feedback, and just shoot the breeze.
One of the advantages of a persistent chat tool like Campfire over other media is that it respects a worker's focus. Clearly, walking over to a coworker's desk and interrupting whatever they are doing doesn't respect that. Similarly with instant messaging, there is an expectation that, if your status is "available", you are going to devote at least half your attention to the conversation. Not responding to an instant message says as much as actually saying something. In other words, it is asynchronous. On the other hand, using email is not real-time enough. Group chat has just the right level of immediacy.
Another advantage of persistent group chat is that having a conversation in the open benefits the rest of the team. The one-to-one nature of IM's and emails create silos of information. The majority of time, the topics people will want to chat about with one person on the team are relevant to the others. Many times, there are multiple people who can chime in on a particular topic or question, and it is valuable to have the answer available for everyone to see. I have frequently searched our chat transcripts to find an answer to a question that I know has been asked before, or to find out who to direct my questions to.
At the very least, this information provides some context to what everyone is up to. The chat logs end up being a running narrative of our company's day-to-day operations. If someone is out for a few days, they can easily browse the transcripts to get up-to-speed on what's been going on, issues that have occurred, company news, etc. This covers 90% of what people need to know. If there is other more critical news, it will communicated in an appropriate form.
Lastly, a key benefit to using group chat is that it's fun. Sharing images and videos is a snap, so it's an obvious forum for LOLcats and other memes.
We also use it to announce free food, birthdays, and off-topic news. It's like a virtual water cooler. Campfire fills a space that isn't covered by email, wikis, instant messaging, and face-to-face meetings. It's often touted as a boon for keeping remote workers on the same page, but the benefits are just as salient for people working in the same location.