I send my bank statements, credit card bills and other documents to my accountant. He produces a return, together with optimisation advice for the coming year. It’s well worth the money. (I also have real estate, private equity, fund interests and emerging trust situations, and am multi-state.)

1. You don't have to figure out which forms to file by yourself. This quickly becomes non-trivial if you run a business, take a lot of deductions, or have weird forms of income.

2. The IRS sees that your return was prepared by a professional, so it is much less likely that they will try for an audit (since a professional will be representing you).

If your tax liability is under $100k and your return is under ~20 pages, you mostly don't need one, but an accountant also doesn't charge much either (about the same price as TurboTax).