Pinned Channels in Chat Window on Desktop
It just came to Mobile App to show pinned channels in the Chat Window.
This is a huge time saver as it is a real pain constantly switching between teams and chat. Having the channels I need to monitor frequently, right at the top of the chat window is huge.
Tom Q. commented
In the mobile app you still can't pin a chat to the top of the chat window, but you can pin a channel and it will appear as pinned in both teams and chat windows.