But what if you need to save up to buy something that you can't afford in one year? Or you're trying to reduce cost in one place enough to hire a team to do some other project?
Then you can argue why you still need the budget. It May make sense to temporarily allocate a bigger budget immediately to do those things instead of delaying, trying to save.
You buy it with financing in that case. And you fit your reductions and hires into the same fiscal year.