Power
You're an accountant with a badge, tasked with looking into the financial records of anyone, anywhere, who may be breaking any kind of tax law. You can arrest someone based solely on your mathematical calculations. This is an incredible amount of power, and you wield it at the behest of the U.S. Treasury Department, arguably the most powerful money management authority in the entire solar system.
As a member of the IRS's Criminal Investigation Division, you comb through records of everyone from multinational corporations to individual campaign contributors, looking for inconsistencies in how they report their money. When you find something, you interview subjects and prepare search warrants (which still legally need to be authorized by a judge, of course).
In your day-to-day, your actions can have a major impact, including exposing a massive money laundering scheme or rooting out funds that are being sent to terrorist organizations. As long as someone is breaking tax and finance laws, you're within your power to investigate those crimes to the fullest extent of the law.