Just had a quick look through. So Final Transmutation, Dwellers, Pit and Purple Sun are out in terms of this being used.
Sadly of course those are the ones you'd want to use it on most.
Still, that leaves every single other spell and there are some doosies! Plus a nifty emergency save against those nasty death spells. I don't have all the books, but I guess this might also help against stuff like plague, curse of years, orc magic, dark elf magic and such too right?