Online features and pricing is totally different form the CD/download version form Costco/ BestBuy.
Online only permits one tax return per account and when a state is purchased e-file state is free. The CD versions allows 5 free Federal e-files and one state download (e-file state is extra).
If you file more then one tax return then usually the CD will be cheaper.
May people prefer online because they do not want to be bothered installing software on there computer or do not have a compatible Mac or Windows computer that can run the software (older Mac's and Windows computers cannot).
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**