The point of these observations is the following tip: The number of balance sheet accounts is usually small in relation to the number of income statement accounts. If you can be certain that the relatively few balance sheet accounts have the correct ending balances, you can have some confidence that the bottom line of the income statement is proper. (The income statement may contain errors—perhaps you entered an amount into the wrong account—but the overall net income has a good chance of being correct.)
I received this tip from a CPA named Bob many years ago, when he helped me to delegate some accounting work. I continue to value his insight.