Originally Posted by andrewrodney
Other than Duotone support, there isn’t anything a PSD provides you can’t get from a TIFF.
I know one other thing; inside InDesign you can freely enable/disable the layers of a linked PSD file; but you cannot do that with a layered TIFF. I think this is more important than duotone support, but like duotone it isn't the most common usage...
An advantage of TIFF over PSD is that it gives you (several) lossless compression options that can help reduce your file size (for large amounts of files this might matter).
Personally I keep flattened files as TIFF w/LZW, layered files as PSD, and copies as JPEG (when low file size is useful). That way it is easy for me to keep track of what is what.