That is the safest way to earn profits from bitcoin but its bit time consuming and risky too as we never know what will be the price very next day. But holding it for long term can be really profitable.
Trading can be really profitable if someone has a good enough capital, with 10 btc someone would earn almost 0.5btc each day if he gets a 5% rise on the coin he is trading, or he should trade with just 5btc and he would get a little less but enough for a day.