The need for screws is important to mount the motherboard on the chassis. On two facts, these screws are different. The first one is comparatively larger higher-end parts to mount the ATX motherboards.
At the same time, the other one is for installing the motherboard relative to the hardware.
Moreover, these are like a coarse thread pitch with a short shaft. Also, it is very forgiving in fastening the machined parts of your PC.
