Two Conductor AC plug (USA).

Once upon a time, both blades were the same size and shape. I should know, my old house is full of those kind of plugs. I have some that are polarized and grounded, but many are still the old symmetrical ones.

Nowadays, everyone has polarized plugs, where one blade is bigger than the other. Unless I dremel down one of the blades, those plugs don't fit in many of my outlets.

So I'm frequently dremeling down blades, cutting off ground pins, or using a ground adapter (with one of the blades dremeled down so it will fit a non-polarized plug).

They all work and I have noticed no ill effects from doing any of the above.

Anyway. My point being... If the AC power is just alternating current, what's the point of polarizing the blades on a two-conductor plug? All the appliances and equipment I've tried works fine the other way around. I can't imagine a situation where it *wouldn't* work the other way around. Is there a such thing as an appliance that must be plugged in with the correct polarity?