Think about it.  If you are saving for retirement, you are trying to save enough in investing to generate enough income to replace your primary salary.  Let’s take my friend’s example above: $50,000 a year.  To generate $50,000, you would need to have almost $1,700,000 saved, and be able to generate a 3% cash flow on that money (which is reasonable if invested in dividend paying stocks).
In equity valuation, residual income represents an economic earnings stream and valuation method for estimating the intrinsic value of a company's common stock. The residual income valuation model values a company as the sum of book value and the present value of expected future residual income. Residual income attempts to measure economic profit, which is the profit remaining after the deduction of opportunity costs for all sources of capital.