Target date mutual funds, or those whose asset mix changes in order to fulfill a fund's target date investment objective, have been a hot innovation in the mutual fund industry in recent years. After all, it's awfully convenient for investors to buy a target date fund based on their retirement yet (or some other goal), plow money into it and not worry about the legwork.
Unfortunately, this is where many investors are in the wrong because they do not do the necessary legwork and simply take the fund's objective at its word. This is a dangerous strategy because as John Bogle points out, many of the funds may own investments that you wouldn't touch on an individual basis.
After all, if a target date fund has a target date of 2050 or beyond, the fund is likely to be very aggressive given its long time horizon. In order to be aggressive, the fund has to take more risks, sometimes more than the investor in the fund realizes. A better option is to find the target date funds which own a basket of index funds whose allocation percentages change as the target date gets closer. In fact, this is what Bogle advocates and as the "father of index investing", who better an authority to trust on the subject?