As far as I can tell from what I heard, the Audigy does not actually record 24-bit files, but it does play them. The Audigy spec sheet is a little misleading.
Standard audio CDs are 16-bit, 44.1 kHz, period.
What's the point of 24-bit? Well, simply put, it's usually a good thing to capture your source with the highest resolution that you can. In the future maybe standard audio stuff will be at 24-bit, and you'll be glad that your source material was recorded there.
That said, there are a lot of arguments about the issues of whether it makes sense to record stuff that does not benefit from the extra resolution (like electric guitars, bass, drums, most voices and most other instruments) since they have energy in the higher frequency parts of the spectrum anyway; others swear that the compromises made by changing the bit depth from 24- to 16-bit prior to burning are worse than the compromises made by just recording at 16 bit in the first place.
If you look through this board over the last few years you'll find a lot of discussion of this issue.