TIFF is the file a retoucher or a print studio often delivers: lossless, with room for more tonal steps than JPEG, and able to keep layers, saved selections and a clipping path. Some marketplaces still list it among their upload formats, a habit from print catalogues, others leave it out, and channels that accept it convert it for display in any case.
Uploading a studio TIFF directly is where things go wrong. The file may be in CMYK, store sixteen bits per channel, carry layers that an upload system flattens in its own way, or hold an extra channel that turns into a stray background. Before upload the file is flattened, converted to RGB at eight bits per channel in sRGB, and exported as JPEG or PNG.
Its size is the other trap. A TIFF can be many times heavier than the JPEG of the same photo, and the compression options inside the format differ: the lossless ones are widely read, while TIFF files that use JPEG compression inside open in some programs and fail in others. Keeping the TIFF as the archive master and exporting a fresh copy for each channel avoids both problems.