When Apple began shipping iMac computers, the amber activity light on the iMac CD-ROM drive was enabled. Initial customer feedback showed that this light was not necessary and detracted from the iMac cosmetically.
When the iMac CD Firmware Update was developed, this light was intentionally disabled via the new firmware to prevent this light from shining through the translucent plastics of the iMac. This was a cosmetic consideration and will not affect any functionality of the CD-ROM drive.
You should only use this update if you are experiencing loud vibrations from a BADLY unbalanced disc. If this behavior is not occurring, then this update is not needed. This application is not required for any other Macintosh systems or CD-ROM drives.