AFAIK when it’s not volatile, the compiler can place it into read-only data segment

True, but preventing that is merely a side effect of the volatile qualifier when applied to any random variable. The reason for volatile's existence is that some memory is changed by the underlying hardware, or by an external process, or by the act of accessing it.

The qualifier was a necessary addition to C in order to support such cases, which you might not encounter if you mainly deal with application code, but you'll see quite a bit in domains like hardware drivers and embedded systems.

A const volatile variable is simply one of these that doesn't accept explicit writes. A sensor output, for example.