That would be the big fluctuation of prices because the volume is not that big compared to forex so a person who holds a big amount can move the market if he wants to and a fluctuation of more than $100 is very possible in just minutes especially if there are fortuitous events. It may work in someone's advantage if he buy something and then the price suddenly shoot up because of some event or announcement so he will gain a bigger profit while most of the time if an event happen like hacking the price will dive and then those who bought when the price is still on top would have bigger losses so it would be a disadvantage. So that is my problem with bitcoin because the price is not that stable yet.