Beware: Many exchanges are especially dodgy, and possibly insolvent. (Bitfinex in particular!) If the market price plummets, the exchange might collapse and you will struggle to get your winnings out...
As I think about it, this is actually another benefit of longing over shorting - it allows you to eliminate the risk of putting value on exchanges, at least if you're okay with limiting your ability to quickly react to market action.
[0]https://medium.com/@bitfinexed/bitfinex-never-repaid-their-t...
[1]https://news.bitcoin.com/bitfinex-bitcoin-cash-deposits-with...