Most organisations reach the same point about two years in. There are more teams than people, half of them have one message in them, and nobody can find the channel where the decision was actually made.
This is not a fault in the software. It is the predictable result of two defaults: anybody can create a team, and nothing ever ends. Four decisions fix it, and none of them need a project.
Decide who can create a team
This single setting causes most of the sprawl. When everybody can create, everybody does, usually for a conversation that should have been a channel in an existing team.
The two workable answers are a short list of people who can create, or anyone can ask and one person creates. Both are fine. What does not work is leaving it open and asking people to be careful.
If you restrict it, say who to ask and promise a turnaround. A request that takes three days pushes people back to email.
Agree a naming convention before the next one is made
Names matter more here than in a folder structure, because the list is flat and searched rather than browsed.
A short prefix that says what the team is for does most of the work. Something for departments, something for projects, something for anything involving people outside the organisation. The exact scheme matters less than having one.
Rename the worst offenders while you are there. Renaming a team is not disruptive and it does not break links to the files inside it.
Decide what happens with people outside the organisation
Guest access is genuinely useful and it is also where most accidental sharing happens. Somebody adds a contractor to a team for one document, the contract ends, and the account stays.
Decide three things. Whether guests are allowed at all. Who approves each one. And how often the list gets reviewed, which can be a calendar reminder rather than a system.
A review every few months, with a named person doing it, catches almost everything. The failure is never that the review was too basic. It is that nobody ever did one.
Give every team an end
This is the decision most organisations skip, and it is the one that prevents the problem returning.
A project team ends when the project does. A department team does not end, but it should still be looked at once a year. Archiving makes a team read only rather than deleting it, and it can be undone, which makes it an easy decision to take.
Archive generously. If somebody needs it back, it takes a minute. If nobody asks in six months, you were right.
The afternoon that clears the backlog
Export the list of teams with their owner and the date of the last message in each. Both are available without any extra tooling.
Then sort by last activity and work from the bottom. Anything with no activity for a year and no owner still at the organisation can be archived without asking. Anything with an owner gets one message asking whether it is still live, and archived if there is no answer within a fortnight.
Most organisations remove between a third and a half of their teams this way, and nobody notices anything except that search works again.
Where files go, and why it matters here
Every team carries a document library behind it, whether anybody uses it or not. That is why archiving a team is not quite the same as tidying a list: the files go read only with it.
Before archiving anything, check whether the files inside are the only copy of something. Usually they are not, and the team was a conversation with a few attachments. Occasionally a team has quietly become where a department keeps its work, and that one needs a decision rather than a tick.
The habit that prevents this is deciding, when a team is created, whether it is a place for conversation or a place for documents. Teams used for both are the ones nobody can archive with confidence two years later.
Two habits worth keeping
Every team has a named owner who still works there. When an owner leaves, the team is reassigned as part of the leaving process rather than discovered ownerless two years later.
And channels rather than teams for anything that is a topic rather than a group of people. A new channel costs nothing and does not add to the list everybody has to scan.
We do this tidy up with the organisations we support, usually in a single session. There is more on our Microsoft 365 page and on modern workplace. If yours has got away from you, tell us roughly how many teams you have and we will say what we would archive first.