the logic is as follows....
good linesmakers have an uncanny ability to predict where the money will go, remember, they do this for a living all day every day.
they can adjust the spread by a point or 2 on any particular game because they usually can tell where public money will flow....
of course their ultimate goal is to get EVEN action, HOWEVER, they are usually SHARPER than the player....
the theory is, if you go against the AVERAGE JOE.... & their 50$ bets.... over the long haul, you shouls come out ahead....
it is only a theory...