I was only trying to say that we can still buy Bitcoins anytime despite the price of our currency against the US dollar since we are holding for long which means our investment in Bitcoin will still be valuable than the amount we bought in Fiats.
You can mean about DCA strategy for Bitcoin investment and this stragegy is useful for many people because you don't have to find best prices and time the market like when is best time for your purchases.
If you apply this strategy, you must manage your finance well generally and your investment capital particularly too. If you can not have capital for DCA with time, this strategy does not work too well for you. Imagine that you buy at ATH, and no longer have money to DCA more in future, your portfolio will be at risk or need a long time to become profitable.
Nobody buy fiats to have profit, and they buy investment assets like gold, silver, bitcoin, real estate. Fiat currencies are inflationary and lose their purchasing powers with time, so they are not investment assets.