Hot switching is permissible allowing for adding and deleting of devices without ever turning a system off. Probably the best reason to consider buying USB peripherals is ease of use for no added price when compared with standard peripherals. Convenience is the name of the game and gone are the days of adding a device and then spending hours figuring out IRQ's or DMA channels. Up to 127 devices can theoretically be attached to one system with nothing to conflict between devices. In fact a system may be kept intact with no justification needed to open a case for a modem or sound card addition.
Flexibility adds another plus.
USB makes it easy to change from one system to another with no messy driver installation. A USB scanner or video camera may be simply unplugged from one computer and then plugged into another without ever turning off the systems. Most new systems purchased today have support for USB built directly into the mother board and all ATX style cases will usually have two ports built into the back of the case. However, if in examining your systems you find no ports this does not mean that your system is not USB compliant. This two-port connector rests in an empty card slot and hooks to the USB connector on the motherboard.