From inSync reader "plhead" comes the following Mac SCSI tip – The Mac constantly polls its internal and external SCSI bus for removable devices that are "empty" i.e. a CD-ROM drive without a CD, or a Jaz drive without a cartridge inside. The Mac will only stop polling when ALL removables are plugged. This polling process can restrict the CPU when it comes to pro audio and video work. So, if you want to really help your Mac out, plug all those removables at all times… floppy, CD-ROM, CD-R, Jaz, Zip, and any others on your system.
Thanks "pl"!