The internal AppleCD 300 may not have a headphone jack or volume control, but it's not entirely featureless. If you unplug the microphone you can record 10 seconds of sound from an audio CD in the Sound Control panel. The switching is automatic, but keep in mind that the files will be huge. When you do this, the Mac mixes the two stereo channels of CD audio to mono and converts them to 8-bit sound, which is similar to what happens with the Quadra's "stereo" input jacks.
In addition, you can boot from the internal CD-ROM, which should significantly ease installing new Systems on those machines. In fact, Apple provides the boot CD instead of a set of System disks. Apparently Apple set this CD up with At Ease to make it even easier to use. The CD contains disk images of the System disks, so users can also make a set of backup disks, just in case. Even though booting from CD will ease the process for users, technical support people should be aware of this difference between normal Macs and Macs with internal CD-ROM players.