What are the top uses of PCIe x1 Slots?

What is the purpose of the PCIe X1 slot pcle x1 slot Expansion-Box with 4x PCIe x1 Slots and PCIe x2 Host Card, for short cards up to 20cm pcle slot Figure shows a motherboard with two x1 PCIe, two x16 PCIe, and three PCI expansion slots Notice that the PCIe x16 slot has a retention

pcle x1 slot In reading the mobo manual, it has the following PCIE slots: • PCIE1 is used for PCIe x1 lane width cards • PCIE2 (PCIe