First of all, in addition to the plain text, you can post links to external websites in the chat
As a participant, besides the simple use of the chat, you also have the possibility to delete your own messages.
As the host of a session, you also have the possibility to delete your own messages and the messages of other participants as seen in the picture below.
Apart from that, as the host, you can delete the entire chat history.
What does this mean? It means that new participants cannot read the "old chat". For them, the chat window appears empty.
But for the "old participants" all messages still exist. Moreover, to you as the host, the chat window will be empty as well.
From this point on, you can no longer delete messages that you have written (for others) because they will no longer be accessible to you.