If you've got a more complex build (GTX video, UAD-2 card/s, multiple M.2 Ultra SSDs), you need to know the details.
Many Z370 motherboards have two M.2 slots.
If you run two M.2 Ultra SSDs (each using 4 PCIe lanes), SATA ports 5/6 are typically disabled.
You can avoid this by putting the 2nd M.2 Ultra SSD on a PCIe "host" card... and installing that in a PCIe slot that has four or more PCIe lanes.
If you run a M.2 Ultra (NVMe) SSD using 2 PCIe lanes, its speed is cut in half.