The original author of this comment (not me, I just imported the code) believed that it improved performance on a given server-side workload.
The person who removed the sleep, Geoff Garen (a colleague and a friend), is a good programmer. I am confident that he read the comment before deleting it. However, his actual performance measurement trumps the comment.
BTW, here is Geoff's snarky response on reading the posts here that mention the comment above the sleep() call: <http://www.quickmeme.com/meme/3qqgwz/>. I agree with him.