Yes there is a difference, but LLC is a legal concept, not a tax one. The IRS taxes sole proprietors the same whether or not they have an LLC.
Tax entities include sole proprietorship (default), partnerships, s corps, c corps. Any of those can be LLCs, but they don't have to.
The IRS doesn't audit annually, companies hire 3rd party auditors. And it's not a tax requirement, it's a public-company requirement.