Bicycle Mechanics - What's the Purpose of this Part?

Took apart my Ultegra 10spd CS-6600 cassette tonight for a good cleaning, and I noticed that there is a paper-thin metal ring between the lock ring and the 12T sprocket. I checked the Shimano web site's exploded view of the cassette and saw this piece is called the "lock ring spacer."

My question is, why is this piece there? I haven't seen anything similar on the few other cassettes I've worked on, and since this spacer separates the notched surfaces on the lockring and the smallest sprocket, it doesn't allow those notches to engage each other. So what's the point of the notched surfaces then, if they aren't allowed to interact?

Please excuse the amateurish question, but I'm curious.

Took apart my Ultegra 10spd CS-6600 cassette tonight for a good cleaning, and I noticed that there is a paper-thin metal ring between the lock ring and the 12T sprocket. I checked the Shimano web site's exploded view of the cassette and saw this piece is called the "lock ring spacer."

My question is, why is this piece there? I haven't seen anything similar on the few other cassettes I've worked on, and since this spacer separates the notched surfaces on the lockring and the smallest sprocket, it doesn't allow those notches to engage each other. So what's the point of the notched surfaces then, if they aren't allowed to interact?

Please excuse the amateurish question, but I'm curious.
Actually, it is thin enough and smaller in diameter than the serrated part of the lockring so it allows the serrations to interact and you will hear the "ratcheting" clicks as the lock ring is tightened.

peek-like Hillrider says it acts like a lock washer.The thin steel distorts-bends in a bit-and pushes on the locking ring so it woun't back out.Luck,Charlie

Thanks for the replies. Makes sense, and definitely makes install and removal a bit easier than on other cassettes I've worked with.