I think it's worth it if you want fast speeds from your cd-rom instead of the A4000's slow onboard IDE
If you have a CS MKII or MKIII you can use the SCSI on the board instead and connect a SCSI cd-rom and get fast transfers and DMA.
I'm using the Fast ata now because I couldn't get a Seagate SCSI hd to work with my SCSI on my CS MKIII no mather what I did...guess I will have to start a topic about it or get another SCSI hd...guess I'm an "IDE-guy" :-)