This is most likely a dumb question, why not use one of the advanced versions of TurboTax?
Because paid tax preparers are required by the IRS to sign the tax return. Since TurboTax is a software to self-prepare tax returns. there is no function for a paid preparer to sign the return.
Furthermore, I would think that most tax professionals would want to put their heads through their computer screens if they had to prepare a tax return on TurboTax. A return that would take me 30 minutes on a professional software would take 2 hours on TurboTax, with 1.5 hours taken up by pressing "Continue."
It's also not particularly price-efficient, either. The Desktop program lets you file 5 federal returns... because after 5, the IRS requires you to get an ERO, because you're clearly a tax preparer! So you'd be stuck with TurboTax Online, which is extremely expensive compared to the E-filing fees on cheaper professional software packages. If I were to use TTO Home and Business today to file a return it would cost me $117 - and the price goes up after March 15.
ProSeries is the professional software that Intuit makes. It shares a few characteristics with the TurboTax Desktop program.
But the main reason is the first one. Any respectable tax preparer will need to sign your tax return as a paid preparer.