Comment by NoboruWataya

It's just a way of keeping track of your finances. If you just have a single bank account and nothing else, then it probably doesn't give you much. But if your assets and liabilities are spread across multiple bank accounts, brokerage accounts, credit cards, loans, P2P/angel investing platforms, etc, then it can be a good way to get a holistic overview of your finances in one place and can help with things like tax returns.

(I don't use beancount but I use GnuCash which is a very similar concept.)