Federal taxes are of course enormously important. They affect every single taxpayer across the nation. Indeed, their reach goes overseas as well, to Americans living abroad or with bank accounts there.
The word "taxes" is a very general one. In practice, there are many different types of taxes. In part, this is because there are so many levels of government: not only federal, but also state and local. It therefore isn't only the decisions of the IRS that can loom large over taxpayers. In California, the decisions of the Franchise Tax Board can do so as well.