An excellent reason to use dollar-cost averaging (DCA) is to minimize volatility risk. Using DCA also removes emotion from the process of saving in bitcoin.
Research shows that using DCA to accumulate bitcoin beats a "buy the dip" strategy:
After analyzing 100 years of S&P 500 monthly prices with 1080 periods of 10-years investment, we can conclude that DCA consistently outperformed Buy the Dip. The median return of DCA was +40% while it was +35% for the second best strategy: Buy the 2% Dip. It seems like there is a correlation between the Dip and the return: the larger the Dip, the lower the return. Also, larger Dips also mean less purchases. - Marc Aragonès Mas
Our favorite illustration of how DCA works is this animation by @w_s_bitcoin that illustrates how saving in bitcoin with consistency allows you to take advantage of bitcoin's volatility to increase your purchasing power over time.