The well known speculator Victor Niederhoffer, in “The Speculator as Hero” describes the benefits of speculation:
Let’s consider some of the principles that explain the causes of shortages and surpluses and the role of speculators. When a harvest is too small to satisfy consumption at its normal rate, speculators come in, hoping to profit from the scarcity by buying. Their purchases raise the price, thereby checking consumption so that the smaller supply will last longer. Producers encouraged by the high price further lessen the shortage by growing or importing to reduce the shortage. On the other side, when the price is higher than the speculators think the facts warrant, they sell. This reduces prices, encouraging consumption and exports and helping to reduce the surplus.
Another service provided by speculators to a market is that by risking their own capital in the hope of profit, they add liquidity to the market and make it easier for others to offset risk, including those who may be classified as hedgers and arbitrageurs.
If a certain market—for example, pork bellies—had no speculators, then only producers (hog farmers) and consumers (butchers, etc.) would participate in that market. With fewer players in the market, there would be a larger spread between the current bid and ask price of pork bellies. Any new entrant in the market who wants to either buy or sell pork bellies would be forced to accept an illiquid market and market prices that have a large bid-ask spread or might even find it difficult to find a co-party to buy or sell to. A speculator (e.g. a pork dealer) may exploit the difference in the spread and, in competition with other speculators, reduce the spread, thus creating a more efficient market.
Speculators also sometimes perform a very important risk bearing role that is beneficial to society. For example, a farmer might be considering planting corn on some unused farmland. Alas, he might not want to do so because he is concerned that the price might fall too far by harvest time. By selling his crop in advance at a fixed price to a speculator, the farmer can hedge the price risk and is now willing to plant the corn. Thus, speculators can actually increase production through their willingness to take on risk.