What is the difference between adding a member to the project area and direct to a team area?

Hi guys,
It seems I can add a team member to a team area, even if he is not added to the project area.
What is the difference? is it only that this member will have permissions related to the team area only but not to project area?

ps: probably I can add because this team member is part of others project areas in the server. I tried also in a sandbox project.