The disadvantage is that LLMs are probabilistic, mercurial, unreliable.

The advantage is that humans are probabilistic, mercurial and unreliable, and LLMs are a way to bridge the gap between humans and machines that, while not wholly reliable, makes the gap much smaller than it used to be.

If you're not making software that interacts with humans or their fuzzy outputs (text, images, voice etc.), and have the luxury of well defined schema, you're not going to see the advantage side.