[yarden.saa]

I am going to give you another perspective;
Since I am in FIRST (starting my 6th year in FRC) the Israeli Regional was 4 days but not really. There is a hour (in some years it was 45 minutes) to load in your stuff. Teams who did not attend the load in has the same amount of time to load in in the next day before everyone can enter the pit area. In both times of load in the teams can take only 5 people including adults to one of the load in times.
Why do they do it?
It's simple, in my opinion, hundreds of people and tons of stuff can be a big mess up. In this configuration, teams can carry their totes/tool and etc... SAFELY!
There are 2 loading times so in average there are half of the teams in load in and the inspectors can handle the bag&tag process without running a marathon.
If teams can't/are not able to attend the load in day, they don't miss a thing.
In my team we prefer to go to the load in day because it is easier to us to transport all of our stuff although we are 45 minutes drive from the venue. The students love to get another day (hour) of the regional spirits!
In one year we could not attend the load in and we didn't felt that we miss something!

edit:
I forgot something important. My team transport our stuff with 2-3 cars. Imagine 50 teams =100-150 cars looking for the closest parking space to the pit area.The load in day makes it less problematic...