At a guess I'd say it enables you to try out different roms without having to continually nandroid backup your current rom and restore it when you don't like the new one or want to try yet another one.

If you don't try different roms very often its probably not worth it.

Should mention its only the Siyah kernel and only for ICS. Will bork your phone if you use a GB rom.

 

I think it's only going to be useful to those who need different ROMs for particular purposes, or perhaps test one extensively while retaining their "daily driver" in case of problems. For anyone simply experimenting with ROMs, nandroid backups will still be less hassle. I can't see myself using it much.

 

It's very useful for rom testing Also, if you feel like a change, it's the quickest way to switch between roms.

 

Is it possible to run two different modems with dual booting?