For those of you still at university I highly suggest taking a few business classes while you get your degree. I took a few in my undergrad days because I was getting a minor in Arts and Cultural Management so my course study was heavy in business classes.
As a freelance designer I have had to us my knowledge from these classes as well as my awesome Microsoft Exel skills quite a bit. One bit reason is you don't always have an assistant to keep your budget up to date, or you ARE that assistant keeping the budget up to date. Knowing what is coming in and what is going out is a big part of the job and already knowing a bit about it and the tools needed is a big step ahead.
Better yet, take an entrepreneurial class if your university offers one. This way you will know more about how to run your freelance business. Knowing if you need to be an LLC, how your taxes work, how to pay yourself, is very important when dealing with real money from real producers.