Transfer data at a faster rate: CP2104 is 2Mbps max, the CP2102N is 3Mbps max
Reprogram the internal settings: CP2104 has a one-time-programmable memory and the CP2102N has reprogrammable settings memory. 99% of people don't use this capability but it is there if you need it.
CP2104 has RS-485 support and GPIO support, CP2102N does not
Long gone are the days of parallel ports and serial ports. Now the USB port reigns supreme! But USB is hard, and you just want to transfer your every-day serial data from a microcontroller to computer. What now? Enter the Adafruit CP2102N Friend!