It is always better to decide how to spend your money before you spend it. Otherwise, your money spends itself and you lose control.
The most important concept in creating a budget is to be conservative with your projected revenue and be liberal with your expenses. In doing that you create a realistic budget and not something that you struggle each month to stay within.
The most common phrase I hear from business owners is, “I don’t know where all my money has gone!” With a good budget you can run a “Budget to Actual” report that will help keep your company on track with how you’ve already decided to spend.
I find that it is rarely how much a company makes that is the problem, but usually always, how much it spends.