Well its optional debranding. In Europe if you buy a phone from Vodafone the phone contains there themes, wallpapers, logos and everything in the software. All Debranding does is simply remove it and put the default Sony Ericsson logos and originals back on.

And the "whole flashing thing" is flash the firmwire to update the firmwire or to debrand.

You need a GENERIC firmwire on the phone to patch.