At the end of June, the bank statement shows €12,480 and the books show €12,705. Working through the unmatched lines, you find a €30 quarterly bank charge that was never recorded and a €195 customer receipt entered by hand and then imported again from the statement.
Recording the charge and deleting the duplicate brings the books to €12,480, matching the statement. Ten minutes of checking has corrected the profit figure, the debtor balance and the cash position at once, which is why reconciliation comes first in every close.
Notice that neither error would have shown up on the VAT return or the profit and loss on its own. Only the comparison with the bank exposed them.