Asset allocation is the biggest driver of portfolio performance, particularly over the long-term. Moreover, it also is reflective of an investor's risk tolerance. The recent financial crisis has negatively impacted investment psychology, particularly among younger investors. As a result, the so-called "Generation-Y" has over half of their assets held in cash -- a "non-earning" asset. While this is safe, there is a risk of loss in value, as cash does not even hold up with inflation. In the long-term, such an allocation means a lower retirement balance--i.e., shortfall risk. Thus, these investors have essentially traded one type of risk for another. See article here, Investment News.
Dolvin, Steven D., "Asset Allocation, Risk Tolerance and Shortfall Risk" (2016). All Chapters. 92.