Most motherboards have a single dedicated M.2 from the CPU, a second one shared with the PCIe 4x slot and some have a third one from the chipset, usually slower

Most motherboards have a single dedicated M.2 from the CPU, a second one shared with the PCIe 4x slot and some have a third one from the chipset, usually slower. If you want a 10 Gbps NIC in your PCI 4x slot, second M.2 is gone and, if you don't have a third one from the chipset then you are limited to a single M.2 and Asus gives you the second one. That's exactly my case with one of the desktops, I would pay $10-20 extra for that extra M.2.