The optimal situation for bookmakers is to set odds that will attract an equal amount of money on both sides, thus limiting their exposure to any one particular result. To further explain, consider two people make a bet on each side of a game without a bookmaker. Each risks $110, meaning there is $220 to be won. The winner of that bet will receive all $220. However, if he had made that $110 bet through a bookmaker he would have only won $100 because of the vig. In a perfect world if all bookmaker action was balanced, they would be guaranteed a nice profit because of the vig.
Moneyline (ML) – form of wagering typically used in baseball and hockey, which replaces the point spread, but also popular in basketball especially for picking underdogs. The team you choose only has to win the game, not win by a certain number of points. The negative value still indicates the favorite (-150) and the positive value indicates the underdog (+130). It's easiest to picture the number 100 sitting in the middle of these two values. For example, if you want to bet a -150 favorite, you would wager $150 in order to win $100. On the underdog, you would risk $100 and win $130 if the underdog wins. It's a simple way to have the risk-reward scenario.