what systems other than temperature control have you used an auto-tune with?

I attempted to use a PID auto-tune on a hydro electric turbine once and watched (with horror) as it stroked the wicket gates open and closed with 10s period for about 30s before the wicket gate linkage actually broke. The linkage breaking was due to improperly set 0-point but it became clear that auto-tune isn't appropriate for all systems, and holy hell I'd be damn sure I knew what an auto-tune was going to do before I unleashed it on actual equipment again. Probably I would want to specify the min and max for the CV ... more knobs that need to be set.

In my avergage hydro-electric plant there are 320 constants or "knobs" for the system plus 170 for each unit, so 1000 parameters that need to be determined during programming or commissioning for a 4-unit plant.

Very good point. Outside of temperature control, I have not seen these used. At my workplace, we have a motor and controller that are presently unusable because the supplier can't come up with workable PID settings. Fortunately it's a demo unit for a prototype, so nobody's out any money.