Answer:
When using a General Ledger, accounts such as Accounts Payable or Accounts Receivable are much easier to work with in the General Ledger if they have a "single" sum of all accounts, in other words for example you have 100 customers that owe you "X" amount of money total. The sum of all the accounts can be listed in the General Ledger, while each specific account detail, i.e customer information, amount owed, etc, can be kept separate in a Subsidiary Ledger.