RAW or Tiff in Photo AI

Just curious! It is recommended that it is preferable to process RAW files in Photo AI and this is what I generally do, however, Tiff files contain the same information as Raw albeit uncompressed so why not use Tiff? Is there any real difference?
The reason I ask is that if I use DPP to adjust exposure for instance I have to save as a Tiff before passing to Photo for noise and sharpening adjustment. I could of course use Photo AI first but it is difficult to see adjustments if photo is underexposed.