I have worked for several organisations with 2k+ users where teams is the primary communication tool.
So far, none of them have used the teams/channels feature due to the fact that, unlike slack, a) you cant add people to channels and people can join/leave channels (so you have no way to know who is "in" a channel, or to communicate to that group) b) you cant add people outside of the "team" and teams are too restrictive.
Instead, they all use chat as channels thusly: create a new chat, add the people you need, rename it, and that becomes the teams channel.
So we all use chat as channels, and teams are not used at all (too rigid, too limiting does not allow proper collaboration/sharing to external partners, slack does everything they need that teams doenst etc)
However, we would like to pin links to the chat, and ideally upload docs. Docs are a problem. The Enterprise 365 office comes with onedrive, but its only for your personal docs. There is no concept of a single, hierarchical company wide document repository replacing our old network drives. Teams-teams has something like this, but no org I have worked with uses teams teams (only teams chat) So we supplement teams with either google docs, dropbox or personal onedrives, and share documents via this method. We would like to be able pin links to such docs in the chats. We cant use the orgs onedrive personal, as it does not allow sharing outside of our org users.
Frequently, we want to schedule a teams meeting with our chat "channel". it would be great to add this option too. There are buttons to start a call, but none to schedule one.
It is worth noting that more than 70% of our communication is with our partners and development teams who are outside of our organisation, and most organisations dont want to have to pay for 365 licenses to communicate with these companies. Some of them have their own teams and 365 licenses, which causes quite a few issues for them communicating with our org we are told, and some are mainly google users (so they schedule meetings in google, we scheduled meetings in teams. the goole ones dont get the nice features like chat which persists after the meeting.
Teams meetings = best in class
Teams chat = best in class
teams teams and channels = worst in class (for organisations I have worked with)