I shoot transparencies when I want to push and pull color film, for the most part.
For portraits, I don't really shoot transparencies, since when I shoot people on film, I generally intend to make type C prints. Usually if I do shoot portraits on transparency film, it is because the transparency is somehow part of the intended presentation (backlit). That usually means at least 6x7 format, but more likely sheet film. I've done portrait "sculptures" on more than one occasion, but it is not common. it is almost always negative film.
Fashion and other products, OTOH, are great with transparency film IMO, because it lets you view and select the images directly, with the characteristics of the film you chose clearly visible. Since I don't often intend to make type C prints from fashion or prouct pix, but will have them scanned in the end, this is a preferable "workflow" to me. Transparencies give you a pretty good idea of what the final product will look like without having to print or scan first. In the cases I do shoot film instead of digital for this subject matter, it is to obtain higher quality than small format digital can offer. That is not needed all that often.
Now, if I shot fashion and still lifes for my own "artistic" uses, I'd probably want the final product to be type C prints, so I'd shoot negative film. But I do not often shoot these things for my own purposes. Shooting them for other people, if it is film at all, it is usually transparencies.