While the sashimono is impressive it's the equivalent to the european surcoat. A way to tell friend from foe as well as being able to identify nobles that can be held for ransom. Belive it or not but being able to take prominent noblemen hostage, and get a nice amount of ransom money for their release, was usually the main reason why noblemen went to battle. It was part of the rules of warfare and big buisness for some of the more martial noble houses. A coat of arms identifying you as a wealthy man was usually a lot better for your health than any armor.
Commoners, of course, were worth nothing and usually met a grim fate indeed if they ended up on the loosing side. Which in turn meant that they had no qualms about slitting the throaths of nobles if they managed to get to them before the knights could "claim" them.
Useless trivia from the Discovery Channel.
