Serial ports on USB allow further use of existing devices, even when the computer doesn't offer serial ports.
The high speed serial port with the 128 byte FIFO allow high speed communication, even in heavy loaded systems. Unique features reduce the system load. The serial port also allows unusual speed settings like 500.000bps.
USB-16COM-M CBL uses a small case due to the high-densitiy DB62 combi connectors for the serial ports. Mounted even in narrow environment, it connects to serial devices via an octopus cables or connection boxes.