Cartel-like (monopoly/oligopoly) pricing leads to a non-optimal outcome (the loss is usually called the deadweight loss). The price is set higher than the socially optimal price - some consumers who would have benefited overall from the good (benefit from good > production cost of good) would not buy and consume the good because the price is higher than the production cost (price of good > benefit from good).

If your curiosity is strong enough, you can find a more detailed outline of the concept in an introductory economic text.