it does everything faster,but its mainlyfor faster communications between modules.

ob2 began "slowing down' around 2000....too many modules talking to each other...one would "brain freeze"...(logic lock is the term)
it was great when we had a pcm,bcm,and airbag module...but when the radio,cluster,keyless entry,dvd,etc all became modules,it was too slow.(they all talked to each other on 1 wire)

engineers finally decided it was not necessary for the dvd player to talk to the brake module,so they split it up with LAN

LAN is a very high speed network with 2 speeds...super high and high.the ecm,bcm,anti-lock,and airbags are on the super high side.(very close to real time)....all others on the other side.(an 08 suburban can have about 22 modules)
And it all has priorities programmed in.....The wheel speed sensors report to the brake module,which ships it to the pcm and cluster....You press the window switch for it to fgo down,the driver door module sends the command to the bcm...in the middle of all this,you hit something...so LAN says screw the window and speed signal..SET OFF THE AIRBAG!

 

Ok makes sense. So each module has a priority and connected to the ECU based on that priority. Like you said with anti-lock brakes, they use the "interstate" connection and the radio would use a separate "two-lane road". Ok got it. And when it came time to add another 22 modules a few years down the road (like the electronic valvetrain idea) they can always add another line to the system.