It's really about the noise, but I doubt it will lower the power consumption.
DiscRotate won't alter your drives firmware, it just sends the drive a command to reduce the speed.
But of course, if you're not having noise-issues then you shouldn't install it.
I also had several reports that it will not work with some drives, that's why I included the DiscRotateTester. It's hard to track down, as Apple only calls them SuperDrives, while in reality they are quite different and not the same manufacture.
For me, it's quite annoying watching a movie on my MBP without reducing the drive speed.