These are accounts designed to prove the balances on other accounts. Typically, you would have a Sales Ledger Control account or a Purchase Ledger Control Account to verify the balances of the total of the Customer Accounts or the Supplier Accounts respectively. They are not necessarily part of the double entry system; but they can be.
In computerised systems they tend to be part of the double entry. Here the double entry of the Sales Daybook comprises a credit to the Sales Account and a debit to the Sales Ledger Control Account. There are still postings made to the Sales Ledger for the customer accounts for the purposes of recoding all customer transactions.
When they are not part of the double entry system it is used to check the main totals e.g. total sales, total refunds and total customer receipts. The balance on this control account should agree to the total balances on the Sales Ledger.