Teams are used solely as a feature in the Chat widget and user lists are a way for the administrators to control and guide the users of a workspace.
Userlists allow the admins to set page visibility limitations, send emails to targeted groups, give the ability to participate in certain widgets, and much more.
Teams allow the participants to write to a chat with one voice without a particular person being singled out. It is a handy tool for facilitators to use when having a session with multiple groups and wanting to hear the thoughts of each group instead of each individual separately.
More information about userlists and how to use them: