Federal Tax Liens can really make your life miserable! When your taxes are not paid the IRS establishes a lien against all of your assets (especially real estate). This gives the IRS the legal right to collect taxes from the sale of your assets, which includes just about everything you own.
Liens filed against you by the IRS also show up on your credit report and often prevent you from opening a checking account, or borrowing against any assets, like your home.
With a Federal Tax lien on your record you can't get a reasonable loan to purchase a car. Think about paying 18-25% interest on a car that is already too expensive. You definitely cannot buy or sell any real estate. The list is endless.