That way, if you have to board a plane late, the overhead space is maxed out and the flight attendants insist that your bag
be taken off the flight and checked, you can easily remove the most valuable item in it - your computer - and have it protected by a padded case when you slip it under the seat in front of you.
This saves space in your bag and enables you to find things readily, since everything is segregated into different carriers.
That will ease your discomfort in case you have to wait a day or so for your bag to catch up with you.
That way, if some other passenger grabs your bag by mistake, or the airline inadvertently sends it to Khartoum, officials will have a better chance of getting it back to you.
This will head off confusion - and the prospect of your bag being carted off by a stranger on the first day of your trip.