Let's say you had enough money to buy 1 whole Bitcoin when the price was at it's lowest in Mar '19 <$3000+> and sold in May '19 <$8600>, then you would have more than doubled your initial investment.
I would rather hold for a longer period of time rather than selling out during those spikes as i am in this market for a long time to understand the market sentiments and i am not putting my credit cards amount in bitcoin to sell off fast, you need to have patience when it comes to any form of investment and the strategy you are telling will work but if the market rises after you sell off then there is no way to enter the market yet again. I do ignore small profits and i am here for the long term and hence it works all the time.
that is a much better approach with investments that have a good long term potential like bitcoin. and i believe that most people who are in bitcoin are adopting this strategy specially since day trading is too much of a hassle for them. the indication of it is also visible on exchanges as they don't grow that much even if the bitcoin adoption grows (lack of day traders but lots of investors).
the strategy that OP suggests is best suitable for altcoin trading in my experience. since altcoins don't have a long term outlook they are best suited for short term trading for you to get in, get the profit and get the hell out. add to that the fact that altcoins only get pumped and dumped and you'll see no other strategy suitable for them.