jtpop's sucks at arguing his point. I'll do it for him.
ADV, college, high school, IFA, medical and training are "set" budgets pre-determined at the beginning of the season. They cannot be changed because their results take effect on Day 1. Coaching, payroll and prospect budgets are essentially cash budgets that are nothing until applied. It's not unusual for a team to expect a coach to ask for 3m then end up getting him for less. The same can be applied to free agents. Once coach hiring and free agency is over, and they take place much later than Day 1, it's possible for a team to have an excess of cash. There's really no reason one shouldn't be able to apply this cash to another category without penalty.
Apply the logic to a trip to the movies. You budget $20 for tickets, $10 for drinks, $6 for popcorn, $4 for Jujubees and pocket a pair of twenties as you walk out the door. Much to your horror, the theater quit carrying Jujubees right after your last trip to the movies(Rambo 2). Your date insists upon some candy. Goobers are $4. You say "Gimme a box of Goobers". Sadly, there's a 50% penalty for switching candies and you only have $2 for Goobers. Your date, angry at your poor planning, throws the drink and popcorn on the ground then storms out. You're forced to watch Hannah Montana's new movie alone. All because you didn't know that the theater stop carrying Jujubees.