In theory NPUs are a cheap, efficient alternative to the GPU for getting good speeds out of larger neural nets. In practice they're rarely used because for simple tasks like blurring, speech to text, noise cancellation, etc you can get usually do it on the CPU just fine. For power users doing really hefty stuff they usually have a GPU anyway so that gets used because it's typically much faster. That's exactly what happens with my AMD AI Max 395+ board. I thought maybe the GPU and NPU could work in parallel but memory limitations mean that's often slower than just using the GPU alone. I think I read that their intended use case for the NPU is background tasks when the GPU is already loaded but that seems like a very niche use case.