Now that Microsoft Teams is here, where does that leave the rest of Microsoft's communications stack? For some parts of it, the overlap is minor or complimentary, but IT admins and users alike are curious what happens to the rest of Microsoft's office communications stack, which the company and its customers has invested billions of dollars in over the years.

Does it all just go away? According to Satya Nadella and Teams project manager, no ... but not everything will be a fit for every team.

In fact, he says the first thing he does in the morning is to check in on Microsoft's Yammer and get a feel for what's going on across his sprawling company.

"Yammer is a bulletin board for the entire organization," he said. "Skype is where instant, real-time communications happen."

Teams chat, he said, works well asynchronously, for more informal, casual conversations.

"What underpins all of these tools is a very powerful platform," said Nadella. "A common identity, a common profile, across all of these tools powered by Azure Active Directory."

Which tool a team uses could vary depending on the context and the type of team.

Nadella put it this way: "There is no universal tool for teams, but a universal toolkit, which we call Office 365."

That said, while Microsoft insisted that it still fully supported its existing collaboration portfolio, it's hard to see a future where more shuffling is not in store. Maybe that means folding Yammer into Teams long-term, or maybe that morphing some of those applications into more focused apps for different kinds of teams, like Project Sonoma, it's experimental chat app built specifically for shift workers.

So how to know if Teams, Yammer, or Skype is the right solution?

Microsoft representatives kept stating that Teams was a good fit for "high-velocity" teams. I'm not sure that's the most helpful metaphor: How many people want to admit to their manager that they're more of a low-velocity worker?

But they also compared Teams to the modern digital equivalent of the open office, a comparison I think  that works a lot better. Open offices help encourage spontaneous collaboration, tend to be less formal, and tend to be more flexible in terms of work assignments as needed.

They also are prone to interruption, can lead to distraction, and can leave teams feeling a little whiplashed at the end of the day if sustained focus is what's needed.

For employees that don't want or need to be constantly "pinging" each other, except when something truly urgent is at hand, Skype for Busines or Yammer might continue to be the best match.

But one interesting challenge is that while Teams is built to be the "open floorplan" of the digital realm, it currently doesn't support guest accounts, and user management is still all done within Active Directory. Control of who gets in and doesn't get in is a key component of maintaining a secure environment, but in cases where you do have a lot of outside collaborators, it's a bit weird that Teams won't work for you (the word is that this kind of user access is slated for early next year).

One other interesting item to note is that cross compatibility between Teams and Microsoft's other offerings is a bit mixed. For many users, Teams may be the best way to interact with SharePoint, ever. But the video and audio calling within teams, for example, isn't cross compatible with Skype for Business, representatives told me, although they emphasized that it was built on the same infrastructure and technology.