It depends on what you are going to use that stick.
With the "pendrivelinux" method - this is basically dd'ing the image to the stick and give it a bootloader - you'll have the original live system. You'll have a standard user with all standard settings (they're setup in /etc/skel/) and you can save files persistently in a casper-rw file or partition. You can also create a new user and so on. As soon as you kill the casper-rw, your pen linux is set back to the original state, like you never did any changes.
A full install will give you just a full #! on a stick. You don't have the limits of the casper-rw filesystem and changes you make are directly applied to the system. If you screw up, you have to reinstall your system like you had to when screwing up a regular OS on a regular HDD.
I'm so meta, even this acronym