Can someone please explain me the utility of TIFF files these agencies offer?

I'm not a contributor..but after a research i think it works something like this: Contributors upload in JPG and agencies convert it in TIFF. (correct me if I'm wrong)

If i'm right: we all know that TIFF is designed to save-export and not lose much quality as JPG do.

So if you made a TIFF from JPG you'll get the same quality, only with greater size in MB. Therefore have no sense!

I leave the word to the experts!
Thanks in advance.

No, DT creates the tiffs on their site. Here are the additional formats you can upload -

The additional format is a file that doubles the price of the maximum raster (JPG) file for that file. Photographers can upload RAW files in the following formats: arw, pmp, srf - Sony ; crw, cr2 - Canon; cmt - Chinon; dcr - Kodak; dng - Digital Negative Format; j6i - Ricoh; mos - Leaf Valeo; mrw - Minolta; nef - Nikon; orf - Olympus; pef - Pentax; raf - Fuji; x3f - Sigma; rw2 - Panasonic Lumix.

Illustrators can upload vectors as cdr- Corel Draw, ai - Adobe Illustrator, eps - Encapsulated Postscript, png - Portable Network Graphics.

So if you made a TIFF from JPG you'll get the same quality, only with greater size in MB. Therefore have no sense!

You got it! I think the idea originally was to overcome the objections of customers of traditional agencies who expected large TIFF files - don't argue with them, just give them what they are asking for. If you have been around a while, agencies like Alamy used to require you to upsize to their minimum (and they knew that was in many cases greater than your camera's native size) where the micros would reject files for upsizing. It was a collision of the old order with the new.

The thing that seems insane is that people today are still buying these - paying extra to have someone else convert the file for you, knowing it's greater than the native size of the item you're buying. I had one (at DT) in late December where they paid 26 credits for TIFF instead of 17 for maximum size.