My friend loves opening different trades at a time, most at times is difficult for him to control what's should be. Trading on free chart with multiple opening can be very dangerous. Yesterday he experience unusual hit when bitcoin price drops again, four trades loss at once when the market go against him. Personally I don't advise multiple trade especially when you're not familiar with trade
Multiple trades up to 4-5 isn't that bad, but what matters here mostly, is the leverage that you are using in trading. But multiple trades is highly discouraged for someone who is managing a small dollar account. so, if one is good in trading, you can use multiple trades at your own advantage because it gonna reduce the number times you will trade by helping you reach your profit target with lesser amount time.
For instance, let's assume you are a kind of trader that's wins 3-4 trades out of every 5 trades it will definitely be in your advantage. But for a newbie trader, it's always best to stick with maximum 2 trades at a time.