What are the limits (if any) of switching a 2-pole load with only one of its poles? Perhaps, if it is an automatic control then it is ok but if it is manual then it is not allowed? Also, does it matter if the single pole switching device is on the unit or in a remote location? For example, a 240v baseboard, electric heater may have a single pole, line-voltage thermostat (either on the heater itself or on the wall). However, take a 208 or 240v, single phase pole-light. Can I control it by a single-pole photocell on a nearby building (no 2-pole contactor or relay in between)? If so, why could I not also have a manual override switch that breaks only one line? Understand that I personally would not do either of these things and consider it "bad practice" whether it is code-compliant or not. Also, anything requiring an actual disconnect would need the breaking of all phase conductors but that is not a case I am considering.

The way I read it you can use a single pole device for control but you still need a 2 pole device for a disconnect anywhere one is required or anything labeled "off".

Good point. I didn't think of the fact that the switch may (but not necessarily) state "off" on it. For instance, a decorative style switch would not and there could not be many circumstances where a pole light requires a disconnect. It still seems as though the code has dropped the ball if a s.p. decora switch is allowed here.

I think the exception is more limited than simply allowing anything to be OK. These are in individual articles on specific pieces of equipment like 424.20(B)

Your single pole switch to a lamp is outlawed here