I know a guy who used to do a lot of 1099 (independent contractor) work and put it all through a shell corporation with himself on the payroll, he claimed it saved him tax money, even after paying an accountant to set up and maintain it.
I see claims like this all the time, but for small businesses (S Corps, sole proprietorships) the "savings" is less than you might think.
Remember a sole proprietorship is not incorporated. You just say "this is my business." As the "owner" you get all of the profits but you are personally responsible for debts. With a sole proprietorship, you (the owner) does not get paid a salary. Instead you pull an "owner's draw" which is what it sounds like: you pull cash out of the business to pay personal expenses. But! For tax purposes, the IRS considers the business's profits (that is, money left over after expenses) to be your income. Your business could net $100,000 but you took a draw for only $25,000 -- this means your personal income is $100,000 and you owe personal income taxes on that (minus various deductions available to regular taxpayers) and you also owe the 15.3% FICA tax in full and the ~4% Medicare tax, too. (Though half of the payroll taxes are a business expense and as such will be deducted from business income.)
It's also worth noting that if you do the sole-proprietor route, your self-employed status means you are required to make quarterly payments of estimated income and payroll taxes.
With an S Corp the IRS requires the owner to pay themselves a "reasonable" W-2 salary. (There's a lot of wiggle room there.) The usual taxes are deducted from the paycheck: Social Security, Medicare, state and federal income taxes. The corporation owner is also allowed to do a draw in the form of a "shareholder distribution." Because of our peculiar tax laws, this distribution is taxed at a lower rate than personal wage income, and they are not subject to withholding for payroll taxes. Also, whatever profit is left over in the business at the end of the year is taxed at the lower corporate rate, not the higher personal rate. This might be where "your guy" is saving money.