Well, from a purely pragmatic perspective of making more profit, it makes sense to buy low, sell high, then buy low again, as long as you can buy it for less than you sold it for. This way, a person can maximize the value if it's done properly. For example, one could buy at $4k in 2017, sell for $18k at the end of that year, and then buy again for, say, $10k in 2018, then sell for $60k in 2021, and so on. This reduces some of the risk because you can cash out when there's good profit, and then just way for the price to fall significantly to buy even more BTC.
But often it's just not worth it to spend time on looking for these patterns, so it's easier to just hodl or do DCA.