Unless you don't care about money at all, playing for cash will make you concentrate more. Ultimately giving you a more intense, focused practice.
That doesn't mean you can't have valuable practice without playing for money.
If you are taking the wrong shot during your practice games will you make the same bad shot when it counts? Likely. I think if you are playing for money, it will make you shoot better shots as well. It doesn't have to be big money at all. A dollar a game will piss you off if you lose too many in a row.
I say play for money, play very cheaply. You will not only be practicing right, but you can also season yourself to knowing what it is like to gamble.
The choice is yours.
I agree 100% with you,i go to play a friend a race to 3in 1pocket,iam the huge favorite, but i lose 3 to 0,i feel like iam trying,but it just isnt the same as when iam betting my money,for the money i would spot him 12 8 and i would get there,no bragging at all thats just the way it is.like u said money makes u do things different weather u notice it or not!