Yamaha's website has a LOT of information on their products and old manuals, 232 codes, and IR codes for their products.
I believe the 3200 came out right before they had a major re-engineer of their products (the 300 series) which improved 232 codes and IR codes.
Really though, if you are using it for a single zone, the 3200 is a very good receiver.
I have not heard of Yamaha ever upgrading their product software. Ever. The 232 port allows serial (text) communication between a computer or control system and the receiver. Products from Crestron and AMX can control the receiver and find out information about the receiver to automate receiver control. With the 300 series of receivers, Yamaha released software to control the components. So, you could set up your receiver entirely by a laptop and the 232 port, then STORE the settings you used in the room. If the receiver ever had problems or needed to go into the shop and came back completely uncalibrated, you could just load the settings from the laptop back into the receiver.
Mostly used for system control though.