What are the top uses of PCIe x1 Slots?

Echo Express Thunderbolt to PCIe Card Expansion Systems pcie expansion slot slot is used by high-demanding expansion cards However, sometimes it becomes pcie slot meaning slot is used by high-demanding expansion cards However, sometimes it becomes

pcie slot function Would a RAID card require cooling if I disconnect the expansion slot cover and use standoffs to mount it to the back of the case?