TIFF vs PSD in Lightroom

I was asked this question during a meet up while discussing/babbling about how I use Lightroom and why I save my Final edits in TIFF Format ... I could not remember why but I had to do some research, I usually don't do things for no reason. PSD files are usually smaller than TIFF files because the PSD format has compression built into it to make the files smaller. This is lossless compression, and doesn't affect the contents of the file - you can open it, save it close it numerous times without affecting the quality of the image it contains. TIFF files are not as compressed (if you choose LZW compression) or aren't compressed at all if you don't compress them, and so are much larger, but contain the same information about the image they contain.

Main reason to use TIFF in Lightroom

1. TIFF has better support for metadata changes/updates.
2. TIFF is publicly documented, PSD is not. That makes TIFF a preferred file format for the long term conservation of digital files.
3. TIFF can save EVERYTHING a PSD can save including layers, paths, channels, transparency, annotations and can go up to 4 GIGS in file size.
4. TIFF can save all the color spaces PSD can.
5. TIFF is better for printing (so I hear)
6. TIFF is public, even if it's owned by Adobe (by virtue of the Aldus purchase). Even if Adobe went belly up tomorrow, TIFF would continue.
7. TIFF files file are not limited to only zip compression and can have many different ways of compression, including jpeg compressed data within a tiff file.

Main issues with PSD in Lightroom

1. PSD cant be saved with Maximum Compatibility as they cant be previewed in Lightroom (kinda negate the work flow benefits of the space savings).
2. PSD is a proprietary format that fewer third party programs can read it.
3. PSB is the new Photoshop "native" file format for images beyond 30,000 pixels.

PSD uses RLE but if you save without the Max compatibility will be a bit smaller, but at the risk of not being able to be used in Lightroom. PSD is a proprietary file format that is NOT a good idea to use in lightroom even some Photoshop engineers will tell you that PSD is no longer the Photoshop "native" file format. It has no advantages and many disadvantages over TIFF.

TIFF (non compressed) is still far more common and universal in the general industry. Unlike past file formats that had no real standard and were implemented differently.
Anybody who thinks PSD is "better" than TIFF is ignorant of the facts. Lightroom did not support PSD in the first beta version and I heard that one of the programers fought tooth and nail to prevent having PSD supported in Lightroom, they lost that fight, but you still can't import a PSD without Max compatibility.

If the files are only going to be used by you, save them as PSD files, but if you're going to exchange them with other photographers or editors, then the TIFF format may be better as it can probably be opened by more different software than can the PSD format.