One could use it to test (embedded) code targetting RISC-V, without needing to use hardware.
Unit tests is the easiest, since they preferably do no I/O. But also integration test by providing an I/O implementation (using a Hardware Abstraction Layer), and driving I/O from the tests.
Such testing is easier to do when one has C access to the simulator, and not having to implement the I/O via some virtual device shuffling bytes etc.
And since its just a C header/library, on can just distribute, include and build the simulator alone with the project/tests. As opposed to relying on the user having qemu (or similar) installed.
I will consider using it for emlearn (a Machine Learning Library for microcontrollers).
This is a full system simulator with an emulated RISC-V CPU in under a 1000 lines of clean C, in two files, so you can include it basically any program (STB style FTW).