In addition to an extra income stream, residual income allows you to diversify your revenue sources. Instead of relying on your standard paycheck, you’re earning money through the royalties of an eBook or the sales of an online course. Diversity of income gives your overall financial portfolio more security and depth. Similar to passive income, residual income gives you more financial stability, flexibility with your lifestyle, additional retirement savings, and a more robust financial standing.
Case Schiller only tracks price appreciation of RE. RE as rental investment vehicle is measured primarily on rental yield or cap rate or some other measure. Price appreciation in that scenario is only a secondary means of growth, and arguably should be ignored as a predictor of returns when deciding on whether or not to invest in rentals. More important key performance indicators for rentals are net operating income and cash ROI. Appreciation, if it occurs, is a bonus.

Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.