Selling your bitcoins is not smart because of the fact that it can bring you in big trouble, I agree about the fact it can be good sometimes but most likely if you are selling to fast you can lose money or make less more profit than you could ever do in the future.
It can bring you a bit in trouble but most of the times it will not and its also that selling is not good because the bitcoin has such a good future a head, it will rise to a very high amount in about 5 years from now, well that is my prediction right now.