In much older versions of the game, when there were a lot of tools available to make or lose money via franchise mode, and some teams were capable of then having HUGE amounts of cash compared to others, the budget aspect made a lot more sense.
These days, I play with it on, but the functionality of it is both mysterious and a fraction of what it used to be. And at least in my experience, when its on, it never seems to change much from season to season with who has money and who does not.