There’s no good reason for you to do a budget. You understand your business’ history. Your labor costs and rents probably won’t change (much), and they’re the biggest cost items you have. And if nothing is going to change, it’s a waste of valuable time and effort.
Before moving on, though, you may want to think about why other successful companies work through the budget process. They don’t want to waste their time any more than you do — maybe there’s something to it after all.