As a manager, you are expected to put together a budget for your department each year. Your compensation may depend, to a large extent, on your ability to stick to that budget. So it’s in your best interest to create a realistic budget when you start out.
http://www.ilmpm.lmmattersonline.com/courses/hmm10/finance_essentials/setting_goals.html
Begin by setting goals. You may want to improve your division’s performance over the previous year, increase net income for the company, or decrease costs—maybe even all three. How do you think your department can accomplish everything it has set out to do? That’s where the budget comes into play. After all, a budget is a plan with numbers.