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The value is:

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).