Right-o. It also allows any gymnast to compete regardless of level although they use Level 10 scoring. Some of the major meets will have 10 sessions and Open sessions and a gym or team can try to enter one or the other - depending on who they want to compete against.
However, the main reason for an Open session is to give international elites the chance to compete during the invitational season. Some of the younger internationals developmentally still need an invitational season and this provides them the opportunity to do so while remaining with their team.