Humey, You're a CPA, what are the most onerous things the IRS can do? Isn't the worst they can do is garnish the wages and place a lien on assets? (aside from forced enlistment).
The IRS can, and does, seize assets & sell them at public auction to resolve unpaid tax obligations. Many a personal residence has been auctioned off to pay taxes. Often the auction take place in front of the home itself. It is humiliating for the delinquent taxpayer, but it happens. IRS can seize your bank account balances (repeatedly, if necessary), leaving you with no money to pay bills. IRS can levy (seize) funds in an IRA, 401k plans, money market, etc., wiping out your retirement savings. If you're self-employed, your accounts receivables can be attached, leaving you with no income. If you get payments/income through credit/debit cards, IRS can levy the merchant processor & you get no income. IRS can show up at your home or place of business accompanied by a tow truck(s), handing you paperwork to seize your vehicle(s). Artwork, jewelry, cash, etc? All can seized to satisfy tax debts. Life insurance with cash loan value can be involuntarily liquidated. If you owe federal taxes & expect to collect Social Security, think again. Uncle Sam isn't keen on paying you benefits at the same time you owe Uncle unpaid taxes. Same goes for military retirement pay. Or any federal funds. You can your passport revoked for having unpaid taxes so forget about that vacation to Aruba (which you shouldn't be taking if have tax debts anyway).
If a business owes delinquent taxes, IRS can show up with a Writ of Entry (civil form of a warrant), seize your business & assets & advertise an auction to sell those assets. You employees are told they're out of work, effective immediately. Customers told to leave the premises at once. Locksmith changes your locks (which you are charged for) & you are ordered out of your own business.
State tax authorities can do everything the IRS does - and more. States grant driver's licenses & professional licenses, i.e. to practice law, practice medicine, be a realtor, electrician, contractor, plumber, taxi driver, a CPA, etc. These licenses can be revoked for unpaid taxes. Then you are really in a world of hurt.
Bottom line: Don't fall behind on taxes. If you do, contact the IRS and/or state (people with money problems often owe both federal & state taxes) and work something out - quickly (those penalties & interest can really add up). If you continue to owe taxes, i.e. not a one time event, you're either a failing business (not enough money to pay all your bills) or a crook.
If you need help & don't understand taxes, it's well worth the money to hire a tax attorney (not your wife's cousin who handles real estate closing, but a TAX lawyer), a CPA or an Enrolled Agent (google the term). I know nothing about cars but how to drive 'em. If something goes wrong, I hire a mechanic. Same principle with tax problems.
I'm in my 30th year employed by the IRS so I've been around the block.