Essentially all books do.
You can manufacturer a -1 line by making two bets:
play the money line (bet 1) and then lay the expected win amount on the -1.5 run line (bet 2)
if if your team wins by 1, you push just like a -1 bet.
if your team wins by 2, you win just as you would a -1 bet.
if your team loses, you lose just as you would a -1 bet.
I was thinking the same thing, but it makes more sense when you use this calculator: http://zcodesystem.com/runline_calc/
Baseball is one of the few sports that's reduced juice everywhere. When you bet -1 -1.5 ect, you are paying 20 cents, or adding at least adding 20 cents when you split up the bet to make the -1/+1 line. Why would anyone do this? Do gamblers hate money?
That is one of few exceptions. On -220 games you're no longer getting reduced juice usually, and very often you're paying 40 cents and even higher, so laying 20 cents on the -1.5 would be the correct move.
As for your second sentence they're correlated that is a fact, so over 1000's of plays paying less vig, on correlated edge, the opne paying less vig, will come out on top.
The manufactured one is sometimes/probably most of the time better because the portion you put on the moneyline is often reduced vigorish. Plus you can line shop, that doesn't change that putting it all on the reduced vig number or best number is the right move over splitting them up.
