Mine is not set to free play. To me it adds to the fun and is nostalgic and yet not really making me more poor.
I enjoy the sound of the quarter dropping into the cash box. Reminds me of my youth and all the time spent in arcades. As mentioned by others, there is something nice about that sound.
I sometimes too use the startegy mentioned above by mystman12 that I can only keep playing if I earn a credit. Keeps me on my toes!
I have a small basket full of quarters in the game area--no one needs to pay (and I don't think anyone has stolen!). Don't have to do it too often but sometimes have to remove quarters to replenish the basket.
And finally I was lucky to have a home machine in my youth (70s era--mom picked it up for a few 100 at some place in downtown LA) that was set to free play. I always wished I could figure out how to make it take quarters (but never did). Now I can!