Matillion ETL allows multiple connections to the same instance. These connections are each given an ID so that each user can see what other connections are doing within the instance (i.e. which job they are editing). For more information on this type of collaboration, see Project Collaboration.
A list of such connections can be found through the 'Manage Connections' menu (Help → Manage Connections).
Each user is listed with their username and current job (the list can be updated using the button at the top-right) and each may be kicked from the instance by another user clicking on the X by their name under the 'End' column. Users cannot kick themselves from the instance. In the example below, a user is being kicked as a precaution to prevent them editing the same job the active user is working on (note how the 'Current Job' is the same for both users).
When the 'End' button is clicked, the corresponding user then receives a warning and may keep their connection if they choose to cancel the disconnection. Thus, Manage Connections is a good way to rid of connections that are idle in order to free up connection slots for other users.
If the countdown completes and the disconnection is not cancelled, this user will be disconnected and left a message to inform them that they were disconnected.
This is like any other disconnect from the instance (such as the instance being restarted) and holds no lasting effect. The same user can immediately refresh the page to reconnect to the instance with no penalty.