The Annual Saving and Withdrawals report shows you the pattern of saving and withdrawals needed in your planning model to keep your per-adult living standard smooth or even year to year.
There are some years where your income exceeds your spending and a saving amount is recommended. Other years you will have more spending than income; in those years you will be dissaving or withdrawing assets from your regular assets in order to keep your discretionary spending smooth.
Remember that you have typically set a dollar amount for existing regular assets (non-retirement assets). This report shows the running balance and the saving and withdrawal pattern for those regular assets. You also indicated some assumed rate of return for that pool of money. This pool of regular assets is assumed to achieve your assigned rate of return through the years.
The interest or earnings for this pool of assets is shown in current-year dollars in the Income Overview report. Often this interest earnings, this income, though reported as income to the IRS in nominal terms, is simply reinvested in the account (not withdrawn). In a year when there is saving recommended, the earnings income is reinvested or allowed to remain in the brokerage or saving account, it counts as saving that year. In other words, earnings or interest unspent equals saving. And if your Annual Saving and Withdrawals report says you should be saving, remember that in most cases, as just described, this interest earned counts toward this saving target. In other words, if your Annual Saving and Withdrawals report indicates to save $4,000 but you also notice that your Income Overview report show that you have $4,000 in earnings, you don't need to save the $4000 assuming that you do not withdraw your interest earnings from your regular asset account.
A simpler way to think about it is to note that if you receive the income you expect per your plan, and if you limit your spending to the spending shown in the Spending Overview report (which includes discretionary spending), the saving or withdrawals will take care of itself because Total Income - Total Spending + or - Saving / Withdrawals always equals $0 in any given year.