2 problems not talked about here that are things I've had to deal with: 1) Month/Quarter close. While this post talks about the account ledger, when you start

2 problems not talked about here that are things I've had to deal with: 1) Month/Quarter close. While this post talks about the account ledger, when you start dealing with a public company that has to report numbers, you have hard-cutoffs and have to make sure everything goes smoothly for month or quarter close. 2) Cash-in-transit accounting: this post assumes your payment processor is 100% correct and nothing goes wrong. When you get big enough, you need to be able to match any money that lands in a bank account with a given invoice/billing entry. You need to be able to detect any invoices that do not have a paired bank statement line. And as others have called out, the reverse can happen where you get paid for something that may not have an invoice item associated with it. Being able to deal with credits on a bank account not associated with a billing invoice can be equally important. Maybe you can say that these are all accounting departments problem, but they are tightly coupled and the 2 teams need to work together that there are no discrepancies between their books.