"u only have to win by one..."
This is true - however if that is the strategy you are using then why not take the +1.5 for every game - not only do you not have to win by one, but you can lose by one!!!
My opinion is that I don't buy this argument, because if you don't really believe the team can win the game comfortably it may not be worth the bet in the first place.
I have experimented with playing both the runline and the ML... Rather than just the same old option of a win or a loss you have three scenarios (1) - a comfortable win results in two wins, (2) a squeaker results in either an even split - a slight negative, or a slight plus in the case where yer playing a dog, and (3) a loss which results in 2 losses.
The way this can be used most efficiently is to play all dogs or only the slightest of favorites. The only problem is that it takes a lot of discipline.
I found out first hand as I went on a massive losing streak and I began questioning the practice - however, I realized that a win more than makes up for a loss if I stick to the dogs.
GL