There are times when I have a file open that I don't want it to "save" and overwrite the existing. Also, on my current setup "saving" takes more than a few seconds especially when the job gets more complex. I don't know how autosave saves it without stopping everything else like a regular "save" does, but I wouldn't like an automatic save to stop everything else whilst saving....
If I had a wish, it would be that the autosave file were more obviously a .pln file. Admittedly, now that I know, it doesn't really matter to me as much anymore...