Here's an example: embedding Python in other applications. Out of the box it's impossible to just start running scripts at will from multiple threads. Which happens to be what our application does, because as you say we want some speed/concurrency so have a backend running multiple threads C#/C++. But on top of that some things are customised in Python, and now we use IronPython which has no GIL so that all just works. Is this a huge game changer? As a whole, no, but for us: yes it would be awesome if we could just use Python.Net (which is just a layer over CPython) out of the box without having to deal with it's GIL.