Function of the coral banded shrimp

[my2rotties]

I was just curious of what benefit these shrimp have to being in a tank? I have one that came in some rocks I bought in a tank shut down, and he is just creepy. He is not killing any of my cleaner or peppermint shrimp even though I read that they do this.

Do they do anything aside of killing small fish and shrimp? To me it does not look like he would be any good at killing anything since he is rather slow and too big to get into small crevices that my shrimp stay in. I have had him three months and I have never seen him eat anything or really do much rather then look creepy.