The point is that these things (string processing/hash tables) are typically done using custom/tuned code in C and so would be faster than the generic, and not particularly carefully tuned Julia implementations.

However, given this library seems to be about passing NumPy arrays to/from Julia, the application is almost certainly to expose numerical stuff from Julia to Python. Basically, the use case is similar to Numba, but it works by producing a C-extension from a Julia system image (if I understand correctly). The main advantage over something like Numba would be access to the Julia ecosystem.