TurboTax Online saves to the cloud; it is step-by-step questions, and by the answers you give, the proper pages/forms will open up for you to enter what you need to claim.  

TurboTax Desktop saves to your desktop. You have a choice to complete your return in easy steps (which is similar to the online version) or choose the Forms mode to put your entries directly on the forms. 

TurboTax Online: you pay per return, whereas TurboTax Desktop has multiple returns; therefore, if you will be doing your spouse's, children's, or friend's return, it will save you money.

Thank you for choosing TurboTax.