A one-sided surge or plunge. Going long on Soxx is better than going short on Soxs. To bet on a rebound, in a volatile downward trend, going short on Soxs is better than going long on Soxx. Look at the prices of Soxx, Soxx, and Soxs yourself. You'll see how much damage can be done. If you're not expecting a one-sided surge, don't buy Soxx to try and catch the bottom. Because if you're shorting Soxs and get trapped, you can wait a few days of consolidation; if the price of Soxx doesn't change, you'll break even, but with Soxs, you'll lose more and more.