8 bit image pov
Advantages: in a word, throughput. Disadvantages: More complications, board layout, more connections, greater cost, etc. Probably not a lot of difference in programming though. For general purpose use, eight bit is fine for most apps. Sixteen bit tends to be used in things like automotive real time ignition processing and other things at the same time. 32 bit, used for things like image processing etc. Check what you need, and read the specs. No point going overboard, you are generally just wasting power and money.