In money market accounts, the bank can use your balance and invest it into other safe investment vehicles where it is expected to grow. (kingofkash.com)
By the time you are ready to retire, the vast majority of your money should be in bonds or other safe investment vehicles. (thecollegeinvestor.com)
Additionally, since the fund is comprised of NASDAQ stocks, it will tend to more more volatile than a broader market index like the S&P 500 and of course, other safe investments with lower volatility that rely on income for net returns rather than capital appreciation. (etfbase.com)