Here are a few benefits of dual-boot:

* safety; do all your experimenting on the boot part of your external card. if you get in trouble, just boot to your flash, and clone again. That way, you will never lose your basic funtionality. This presumes you have a well-equipped flash setup to start with.
* More space in the filesystem, but this is true only if your external SD card is bigger.

re: learning more...
My clone adventures:
http://www.internettablettalk.com/fo...025#post194025
Some links:
http://www.internettablettalk.com/fo...ad.php?t=20818
Things I've been able to do:
http://www.internettablettalk.com/fo...ad.php?t=20702
Tips on root access:
http://www.internettablettalk.com/fo...ad.php?t=20670

Steve