When should I click the Auto-terminate checkbox?
Core defaults memberships to auto renew. If you want a membership to not auto renew, you want it to auto terminate. The most common scenario for these are long term memberships (Semi-annuals or Annuals) where at the end of the cycle you want the unit to terminate. Some membership types can be set so they always auto-terminate. For example, 1 week memberships are usually forced to auto-terminate at the end of the week. If you cannot uncheck the box it's because the membership type is set to never auto-renew.