If you're holding bitcoin for long term you might specify for how long I should hold my Bitcoin, is it for 5 years, 10 years or so. But if you're holding Bitcoin for short term you should sell them once the price is going up, yeah buy low and sell high. I personally hold Bitcoin as a long term investment, even if the price is going up I don't sell my coins because I have specified the period for holding Bitcoin. when the time comes and the price is skyrocket I will sell those coins.
It maybe we are different, I consider myself as a short term holder and just like what you've said...I sell my Bitcoins when seeing profits on it and buy back again. That was what I usually do and also I feel that it helps me to generate more gain rather than to be a long-term holder. I understand the risk of this and that it why it needs to be smart in doing decision.