Comment by arpinum

There are scenarios where these target date funds are not good.

Rebalancing into bonds and mmmfs is a form of insurance against catastrophic losses equities. But if you have a sufficiently large account then catastrophic losses that affect your life are extremely rare, if they do occur they will likely affect your bond portfolio as well, and the expected loss vs 100% equities over 15-20 years is significant, something like 10x the value of the insurance you are buying.

If you want insurance for a large account then long-dated put options 20% of the money are much cheaper.