How does bag transfer work?
 

I always have this curiosity: how does the bag transfer process work? What is the SOP for United?

For example, at the connecting airport, does my bag go back to the baggage sorting system in the airport before it ends up on the aircraft of my next flight? In addition, when the aircraft for my next flight happens to park at the next gate, and my connecting is short, will they simply walk my bag over to the next gate? Thanks!

I think it is really going to depend somewhat on the airport and also the length of the connection. Your bag usually can make a much shorter connection then you. Airports do have expediting processes and sometimes you'll see a bag handler going from plane to plane to drop off these short connection bags.