Knowing whether a hum is 60Hz or not tells you whether it's a ground loop or some other problem. For crosstalk a lot of mixers have a 1khz sine tone generator. It's useful to be able to verify that you're dealing with a particular frequency. You are not always able to rely on your ears to the extent that you'd like when you're in the field, since the environment where a PA is being set up can be noisy as well.
This device has a few other tricks up its sleeve as well as a basic 'scope; it also does FFT, phase metering, and operates as a voltmeter. I'm not suggesting it's the ultimate device of its kind, just pointing out that there is a class of people for whom having this functionality in a highly portable package would in fact be handy.
Oh, and the protocol sniffer means you can test MIDI output from a synth or sequencer.
This device has a few other tricks up its sleeve as well as a basic 'scope; it also does FFT, phase metering, and operates as a voltmeter. I'm not suggesting it's the ultimate device of its kind, just pointing out that there is a class of people for whom having this functionality in a highly portable package would in fact be handy.
Oh, and the protocol sniffer means you can test MIDI output from a synth or sequencer.