Well, for those people that do not have a Hi-Def TV or Cable/SAT, all the converter box will do is allow you to still get your local TV stations after the transition this month.
You can still use a regular antenna with the box. Plus, you get the cool new feature of a program guide for free.
...of course you are limited to about 5 channels. But, with the crap on TV now a days, 5 is more than enough.