If we assume that a balanced budget is a good thing, then we assume that we don’t have unlimited funds. Based on that assumption, then we are talking about how to spend the funds that we do have.
It’s certainly possible to argue that governments should spend without constraint (i.e., deficits don’t matter). In that case, there is no such thing as scarce funds. However, if we don’t accept that argument, then the funds to spend are limited and we need to prioritise accordingly.