One handy thing with a tuner with a built-in mike is that you can check what key you feel like singing a particular song in tonight while you are on your way there, without any instrument to distort things. I find the right key for the same song can vary enormously, according to the state of me vocal chords. (Thank god for capos.)

Electronic tuners provide an independent standard for a group of potentially quarrelsome musicians.

I've sometimes imagined what would happen if some pissed-off employee in the factory making them sent out a batch tuned sharp or flat. Bloodshed in the sessions.