Well, it will depend on how much longer you will hold after buying. This strategy I used when I want to sell my token on the exchange at set a higher amount. Indeed, --this is not a bad idea and you are safe about this. But I think there are a few disadvantages that I have seen on this strategy. First, never leave your Bitcoin on the exchange and second, it might you lose from fees. My good advice is, buy Bitcoin and store it in the long term purpose until you will see your profit.