Indeed. While dr==cr gets you far towards being able to calculate account balances and an entity's aggregate financial position, it's also fairly foundational that you are able calculate the company's position with different counterparties. So knowing that Alice purchased the book from Foo Booksellers, but maybe hasn't settled with FooBooks yet is super relevant.

The company's accountant may care about balances and reconciling them back to things like the existence of said book, a receipt for payment or a bank transaction indicating settlement happened. At a big enough company, the accounts payables nerds may come along and be focused on making sure the full process procuring and paying has happened correctly, including record-keeping, tax compliance, and the actual movement of funds.

When you start to scale how all of these processes are executed and recorded, it's dense enough that it still surprises me many years later.