This is a huge difference. The potential profit on the moneyline wager ($143) is over 40% greater than that of the point spread wager ($100). You're a little less likely to win, as there is a chance that Seattle would lose by one or two points, but there's a more than fair chance that if they did cover they would actually win the match. And, of course, if they lost by three or more then you'd have lost either way.
Understand that negative odds indicate how much money your must spend to make $100. When betting on the favorite, you take less risk, and thus earn less. When betting on a favorite, the moneyline is the amount of money you need to spend to make $100 profit. In the previous example, in order to make $100 of profit betting for the Cowboys, you would need to spend $135. Like positive odds, you earn back your bet when winning.
Sports betting has been around since 1000 B.C in China, where betting on animal fights was commonplace. In ancient Rome, one could wager on the Gladiatorial games. The idea of betting on sports is as old as organized sport itself. But up until the 1940s, bettors were fairly limited in what kind of bets they could make. The standard system of odds would allow bets on, for example, the 3-1 odds that the Steelers would beat the Browns.