Businesses are not families, and I know lots of families that do spend their budgets like that. In fact my wife and I realized that we came in $5000 under our annual budget and are looking at things we could buy that would improve our life that we didn't think we could afford earlier.

Companies generally already have cash stores, but cash sitting is cash wasted. Cash can and should be invested, either back in the company, or elsewhere, used to pay down debt, or used to pay shareholders.

So if your budget is reduced because you didn't spend it. That money will not just sit for a rainy day, it will be transferred to another place where it can do work for the business.

A last example. Microsoft purchased Minecraft, because it had too much cash in the bank, and the interest return on that cash was less than they would get by buying Minecraft, so they did.