Comment by mrngm

I found this document[0] very insightful. It's quite a long read, but gradually introduces the concepts needed for double-entry bookkeeping.

I think the main advantage is that you can granularly keep track of the movement of money, stocks, commodities, etc., and their conversions. As a day-to-day example, it gives you the ability to follow, for example, invoices received (Liabilities or Accounts Payable), transactions on a bank account (Assets), and what you are going to spend (or at some point, have spent) (Expenses).

This separation allows you to, for example, enter an invoice you've received on January 1 in Accounts Payable, with a corresponding value in Expenses. At this moment, nothing happened yet, it's simply an administrative transfer of some amount from an asset account to an expenses account (the sum of these transfers must be zero, so one amount is negative whereas the other amount is positive. See [0] for more details).

As a result, this gives you insight in what still needs to be paid. Once a transaction for that invoice enters your bank account on, for example, January 10, it gets "paid" to Accounts Payable, thus giving you a link between an invoice, its payment, and finally the amount spent. (This concept also works the other way around, see this sibling comment[1], where it's also extended into working with multiple accounts.)

[0] https://news.ycombinator.com/item?id=46464893