There are few different commands to delete elements.
Delete Elements - will delete all elements inserted with Smart Connections. Manually placed elements will not be deleted.
Delete Selected - you have to select one element and this command will delete all of inserts from that one Detail Priority tab. All the others will remain.
Delete All - will delete all hosted elements, both manually placed and placed with Smart Connections.
Delete w/o Host - will delete all details that have lost their hosts.