In theory, sportsbooks don't care about the outcome of a game, although for those of you who bet on the Steelers (-5.5) last season versus the Chargers and saw a game winning TD returned by S Troy Palumalu as the game expired reversed, thus negating a seven point victory and putting the final at 11-10, you might think otherwise, but this is how it's supposed to be.
For example, if you’re betting on teams A, B, and C to win outright, you’ll have two round robin options available. Your By 2’s option includes all possible 2-team parlays for these three wagers (A+B, B+C, and A+C). And your By 3’s option includes all possible 3-team parlays on these 3 wagers (A+B+C). If you wager $30 on the By 2’s option, that money will be split evenly among the 2-team parlays ($10 on each of the 3 wagers).
In this instance, the Dodgers are the favored team, as signified by the negative numeral. It would cost you $130 in order to collect a $100 payout on a Dodgers victory (plus the original wager of $130). But if you bet $100 on the Cubs, you'd collect $120 if they win (plus the original wager). In other words, you'll have to wager more money on Los Angeles than you would Chicago in order collect $100 on a bet.
This is a very common occurrence in sports betting and sportsbooks have the full right to shift the spread or odds for any given match prior to it starting. Many factors can influence a change of the spread such as injuries, the number of bets coming in for either team or the weather, to name a few. Depending on the timing of placing the bet, the bettor can also have an advantage or a disadvantage depending on which way the spread has shifted.