For many projects with light dependencies it’s relatively easy to build them all from source. But building NumPy, Cython, or wheels in the Geospatial field can sometimes be more complex, or just time consuming, especially in CI.
By allowing pre-release wheels to be uploaded earlier, it allows downstream dependencies of those project to start testing new Python versions without having to build all dependencies from source.
In this thread I go into it a lot deeper: Create system to recognize, manage and install non-ABI-stable Python wheels (created with alpha/beta versions of Python)