RDMS databases are not a weak point. A bad model of your transaction is a weak point. Depending on the application, and not all applications require this, you may need a consistent read state for the data. Eventually consistent is like saying periodically wrong. Let's say a trader enters a trade for that exceeds there allowed VAR, because they looked at their screen thought they had more dry powder. (Cocaine jokes aside). That becomes a risk management problem. (Also the risk that traders can just use the 'It said I was below my limit' excuse).

If you want an example where consistency is not important, you might be able to overdraw from your bank with your ATM card. The bank is happy for this to be inconsistent, since they can charge for the overdraft.