i think anther scenario is more likely: you say you need a 1 million budget to run the IT department, but you only spend part of it, then next year if you ask for 1 million again, they will say, but last year you only spent 700k, so we are going to give you only that much.

but the problem here is how budgets are assigned. instead of a fixed number it should have a lower and an upper bound. at least X, but no more than Y. the closer to you get the better, but next year the budget will be the same range. only if you drop below X you run into the above problem, but then it's much less likely and if you really spend that little something else is wrong or the budget really was to high.