First, it shows the equivalence of the economic accounts concept of capital consumption and of economic depreciation.
An important empirical implication of equation (3a) is: Any empirical method that is appropriate for estimating economic depreciation is also appropriate for estimating capital consumption in economic accounts, for economic depreciation and capital consumption are identical.
Denison  argued that the standard definition of economic depreciation, which corresponds to equation (3a), does not provide the appropriate measure of capital consumption in economic accounts because, he maintained, capital consumption should be allocated to production over the capital good's lifetime in proportion to capital used up in production.
Where there is no decay, capital used up consists only of exhaustions; because the present value of lightbulb exhaustions equals the loss in value of a one-period older bulb, this loss in value equals capital consumption, and is also exactly the definition of economic depreciation.
Capital consumption is the appropriate one-period adjustment for a wealth measure, and therefore appropriately determines the difference between GDP and net domestic product.
Suppose new investment offsets the value of light-bulb exhaustions (as required by the economic accounts definition of capital consumption, when there is no decay).