Well, personally, it would be nice to carry a device that can be both my smartphone as well as my tablet. Continued innovation in this field could even make such a device your laptop replacement as well. So, 1 device would be able to do the work of 3 devices.

As for the thickness, the latest phones are 7-8.5 mm in thickness. Sure, the foldable phones would be thicker in the initial stages, but just like the smartphone's evolution, they too will become thinner and lighter in the future, and it wouldn't take much time because they would have more internal space to work with, so they can really spread the electronics in the X and Y axis without needing to use much of the Z axis.

At the end, it's always up to the market to decide the success of any new tech, based on several factors and the same will apply to foldable phones as well.