The four types of special journals are sales journals, cash receipts journals, purchase journals, and cash payments journals. These special journals are typically designed to make simple records of the transactions that are used the most. The advantage of using these journals is having only one type of transaction per journal so at a later time, during the accounting process, it is easier to find the transactions instead of having to sift through everything to find one specific thing. You would use these journals when the transaction occurs and record it in the correct journal.
A subsidiary ledger is a number of similar accounts whose total equals the amount in the general ledger. The purpose of a subsidiary ledger would be to keep better track and control of the financial information. Subsidiary ledgers make the information more organized.
A control account is the accounts receivable and accounts and accounts payable whose balance should equal the general ledgers total, thus equaling the subsidiary ledger. The purpose of the control account is to have all the correct totals, but not have all the details like a subsidiary ledger would have. The purpose is to basically have the numbers, not the details. Again it makes the accounting process less complicated.
Some advantages of subsidiary ledgers are to rid the general ledger of all the details; it provides information on specific accounts, it shows each transaction so it can help with errors, and it generally helps with all the record keeping because it is all in separate ledgers and easier to track.