Topics are intended to be short-lived. This is different from a chat room in regular chat applications: chat rooms go on for ever and ever.
The goal of a single topic is to answer a question, solve a problem, and in general: get stuff done.
Once the goal of the topic has been achieved, it is best practice to close it immediately.
Any participant on the topic can propose to close the topic by using the slash command /close.
Once a participant closes the topic, it is clearly indicated to other participants that the topic is closed (the topic is crossed out in the topic list).
If you agree that the topic should be closed, simply Acknowledge (using the checkmark) the Topic. The Topic will now be removed from your Inbox and Open Topic lists. It is then safely stored in your topic archive.
If you think the topic is not yet ready to close, simply add a new comment. This will re-open the topic for all participants.
It is recommended to add the conclusion of the topic as the last comment. You can do this by adding the conclusion after the slash command. For example: /close it has been agreed that the new homepage will be green. This makes it easy for future readers to quickly discover the conclusion of a (possibly long) discussion.
If you are not yet sure if the topic should be closed, it's safe to type /close anyways.. other participants can easily re-open the topic if necessary by adding new comments.