( I can hardly believe I am posting that .... )
One reason for having 100kHz or more available on an "Audio Generator" is to enable the testing of audio filters that may have turn over frequencies at say 22 kHz. To find the roll of slope, one needs to check the response for several octaves above that frequency.
Another use is in testing the response of audio transformers - ie line, mic or valve output. These often exhibit severe ringing at frequencies between 25 kHz and 150kHz. This can often be eliminated with a suitable RC damping network.
Audio gens also need to go down to 1 or 2 Hz as well - so one can check any sub sonic filters included in amplifiers and other devices OR to force DC and anti-thump protection relays in power amps to cycle to verify their operation.
Many other good reasons exist too.
.... Phil