Legal insider trading helps make the stock market more efficient. By studying over 59,000 insider trades from 1995 to 1999, researchers found that insider trading leads to mild changes in stock prices. Insiders seem to have good timing in buying and selling stocks, affecting market liquidity. On days when insiders buy, market liquidity decreases, while it increases on days when they sell. This suggests that insiders help speed up price discovery in the market.