A typical book might be 100% long and 50% short, leaving 50% net exposure and 150% gross. Net exposure determines market sensitivity; gross exposure determines how much stock-specific risk and financing cost the book carries.
The short side is not simply a mirror of the long side. Shorts face borrow costs, recall risk, unlimited theoretical loss, and position sizes that grow as the trade moves against you, which makes them operationally harder to hold. See short-selling and hard-to-borrow.
Investors should decompose returns before paying for them. If a 60% net long book returns roughly what 0.6 times the index returned, the manager delivered beta at active fees rather than stock selection. See market-neutral.
Related: market-neutral, short-selling, hard-to-borrow, beta, hedge-fund, pairs-trading