Shorting only makes sense if you do leverage, which at the same time leverage never makes sense because you can get on debt if things go against you.
Basically never short. Buy and hold. You require too much luck to win shorting. I dont believe in predicting the market, let alone small market noise.
It's impossible to go into debt with Coinarch, hence the reason why they are different from other trading platforms.
Obviously, if you guess the correct bitcoin movement i.e. if you think it will increase and it does, then you profit. If you guess incorrectly you only lose what you invest. You don't have to invest anymore. So if you invest $10 and leverage 10x it basically means you have 100 worth of bitcoins. If you guess incorrectly you will only lose $10 as opposed to losing $100. Though if you guessed correctly and the price moved 10% you would reap the rewards, you would profit $10, doubling your money.
Does this make sense? You should give it a try - sounds like you could make a lot of money.