Yeah, it is supposed to help performance. How much, I don't know.
If you disable it, caching is not used, and you don't take the risk of losing or corrupting data on a bad shutdown. I think that means that if disabled. all write operations go directly to the disk (not to the cache). Since they go to the disk directly, you don't have the risk of corruption. If enabled, and you had a bad shutdown, the data sitting in the cache has not yet been written to disk and could be lost. That's my feeble attempt at understanding.
You could easily download HD Tune and do some tests with it off and on to see how much difference it makes. Matter of fact, I might try that myself.