The product bundles asset allocation, rebalancing and manager selection into one holding, which removes most of the ways an investor can damage a long-horizon plan through inattention or panic.
Differences between funds with the same date are larger than most buyers expect. Two 2050 funds might hold 88% and 96% equities, use different glide-path shapes, and charge 0.10% versus 0.65%. On a $300,000 balance that fee gap is $1,650 a year, compounding against the investor for decades.
A target date fund also assumes the date is the only thing that matters. It knows nothing about other assets, tax position, or risk tolerance, so holding one alongside a separate equity portfolio can quietly produce an allocation nobody chose. See glide-path and total-expense-ratio.
Related: glide-path, asset-allocation