This basically what I always try to do, not just with cryptos. Buy low sell high. But for me is much easier to just trade my OTC where I can get into and out of a position in a split second if I want to. Assuring a much better price compared to buying the real thing which takes some time.
This is the difference investing to hodl and trading for quick bucks
RE: important BTC update 21.09.17 - why you should hope for a fast freefall