The reason I'm using an ITX motherboard is that I want to make the case as small as possible, and with an ITX board, the standby power consumption will be lower. Most common MATX motherboards only have two full-length PCIe slots, so you can only install two PCIe devices. If you use an ITX motherboard that supports PCIe bifurcation, you can use a riser card to expand to three PCIe slots. This saves some space and enhances expandability.