there are lots of different strategies when it comes to investment and managing your money. it is not really easy to say if one strategy is good and the other bad. not generally anyways. sometimes this strategy you described is a good one for certain coins under certain circumstances but not good always.
I usually use this strategy if I want to get the money out for good. meaning if I see the risks of investing in some coin is high so I cash out the initial investment and keep the profit and then continue working with that. and never invest that initial amount ($100 in this case) back in it. and it is a viable strategy!
but in some cases for example when investing in bitcoin I invest the profit back in. in other words I keep the profit in bitcoin not in fiat. for example I buy 0.01BTC price goes up and I expect a correction, I sell and buy back in the dip with the money I got and receive 0.013BTC
Yeah I could see where some coins, it would be a bad idea. But when you say:
And never invest that initial amount ($100 in this case) back in it.
Do you mean that you never invest what you made, back in? That $100 that you skimmed off the top, never goes back in? But what if its a solid coin? That you know is just going to go right back up, after the market recovers from the crash?