Every workspace has some channels in which announcements or general messages are posted which are to be of everyone's attention. And when new members join a workspace, it becomes a tedious job to add them to these channels. So we have Default Channels.
This feature allows the admin of the workspace to turn channels to Default by which every member added to the workspace becomes a member of these channels automatically.
How it works:
When a workspace is created, a default channel by the workspace name is automatically created.
The admin can manage default channels from the Channels section in the sidebar.
Click on the Settings icon on the top right.
Search the name of the channel that you want to make default. Click on the Make as default button.
You can also remove the channels from default by the Remove button.
You don't need to explicitly add every member. By using default channel feature, you can quickly create channels that have all the members of your workspace.
Check out this video to see more in details - https://youtu.be/6wP7wn9E0Lc