What are ledgers used for?
Subsidiary ledgers contain the detail that support the general
ledger accounts. For example, the general ledger account, "Accounts
Receivable" might have a balance of $230. This is the total of all
the subsidiary accounts receivable ledgers. So, there would be a
subsidiary ledger for John Smith (balance $100), Sam Jones (balance
$80) and a subsidiary ledger for George Washington (balance $50).
When George pays us the $50 he owes us, we would record it in his
subsidiary ledger. That brings George's balance down to $0 and the
general ledger account would now be $180 (the total of the two
subsidiary ledgers with balances in them).
Reasons for subsidiary ledgers: You have to record George's
payment as a reduction in what George owe us. If you posted his $50
payment in the general ledger, very quickly you would forget who
paid it to you. Also, by looking at the entries in George's
subsidiary ledger, you can see what he has charged, what he has
paid, and when he has paid. The general ledger is nothing more than
the total of the balances in the subsidiary ledgers. The subsidiary
ledgers have all the detail.