You can do that too if you want. From what I've learned, if you're aggressive at youth, you're 401k takes a dive, you still have time on your back to recover from the damage until when you retire.
But if you're nearing retirement, lets say in 2-5 yrs, you're aggressive 3-4 401k funds takes a dive, you're basically screwed, you only have 2-5 years to try to recover as much as you can, really that's not enough time to recover depending on how bad your account was hit. If this happens, you won't retire early or on time But, if you're conservative 3-4 401k funds takes a dive nearing retirement, the damage won't be as bad. You still lose some money but not as much as, if you had an aggressive flavor nearing retirement. Am I making any sense? This is what I have learned. But to each their own.