If you check the Summary box on an existing account, the account maintains its posted transactions, but you cannot post additional transactions to the account. The account also becomes inactive, but its children accounts maintain their current state.
If you clear the Summary box on an inactive, parent summary account and then save the record, the account is not automatically reactivated nor are its children automatically inactivated. To automatically inactivate the children accounts, first edit the account record to clear the Inactive box and then save the record. Second, edit the account record again to check the Inactive box and then save the record. All children accounts are updated to inactive status.