It protect account balance remain in nature

For example we have a bank account with balance is 0 and nature to debtor

In control during fiscal year:
If we try to create move line for that account with credit value, we should get error that "The nature of the account is not respected" and prevent from save action
I suggest that its a good idea to control is better to happen on reconciliation

In control at the end of fiscal year:
if we try to create account move for closing account and bank account balance is credit, we should get that error too, and its the part of closing fiscal year process

It help us to control to order of income and outcome of that account (the bank) is same as bank statements

to be clear, image what if we don't have stock control in product but we want to prevent sale unavailable products!