[just_for_you]

That's due to Photoshop embedding a variant of the PSD format within the TIFF file, inside its own private TIFF tag.

I'd argue that's even worse than just using PSD by itself. If you open a PSD-inside-TIFF file in an image editor that doesn't recognize that PSD data or which discards unknown TIFF tags when saving, you'll end up having the PSD data getting stripped simply by saving.

Another problem is there might be a mismatch between the TIFF raster data and the embedded PSD document attached. For example someone could open the file in a PSD-unaware editor, make changes, and save the file only making changes to the TIFF raster data. Then later, when someone opens the file in Photshop, they won't see the changes because Photoshop ignored the newer TIFF raster data and used the older, embedded PSD document within it instead.