Problem working on raw files in photoshop cs5?

I can open raw files in photoshop but after I edit them, I save them as the .raw file extension and then I can't reopen them properly in photoshop. What is the point of the .raw file extension in photoshop if u can't open with it after. I thought that it was best to keep your photo in the raw format until u have completely finished editing then save as TIFF.