Here's one for you:
A lot of electrical items have little LED indicators to tell you the status of them, but my hair dryer has a little green one that comes on when it's working.  
Surely the fact that hot air is coming out of it gives the game away.!  

Eliminates the incoming power being the problem why it’s not blowing. If light is on then your problem is elsewhere. Doesn’t seem like much for diagnosis but it helps a bit.

Eliminates the incoming power being the problem why it’s not blowing. If light is on then your problem is elsewhere. Doesn’t seem like much for diagnosis but it helps a bit.

Having it still seems pointless, if the LED comes on and no air comes out, then as a totally sealed unit you will have to buy a new one.
Therefore pointless. 

Well, yes. At least you didn’t waste time trying to find some other confirmed working device to plug into the outlet the hair dryer was plugged into. Or digging out the multimeter to check fuse (I think UK has fuses in plugs).

Light’s on but not blowing? Into the e-waste bin you go. 5 seconds to decide that rather than minutes to test outlet and fuse.

Well, yes. At least you didn’t waste time trying to find some other confirmed working device to plug into the outlet the hair dryer was plugged into. Or digging out the multimeter to check fuse (I think UK has fuses in plugs).

Light’s on but not blowing? Into the e-waste bin you go. 5 seconds to decide that rather than minutes to test outlet and fuse.

Fair point.

Hair dryers have a thermal cutout switch in case of overheat - Some have 2, one at lower temperature that is self resetting, and one at high temperature that blows once for good

I dont know if it cuts only the heater or both heater and fan, but lets assume it cuts both... Then there may be a case when the dryer overheated (due to abuse like blocking the air path) and cut off, now the user puts it away while it is not blowing but will start as soon as the switch resets

Now add some idiots that leave it plugged in and stuff it into drawers... (FFS i seen a guide online how to make a receptacle inside a drawer to have a dryer plugged in)

Not as pointless now is it ?

Well, yes. At least you didn’t waste time trying to find some other confirmed working device to plug into the outlet the hair dryer was plugged into. Or digging out the multimeter to check fuse (I think UK has fuses in plugs).

Light’s on but not blowing? Into the e-waste bin you go. 5 seconds to decide that rather than minutes to test outlet and fuse.

MK plugs used to have a test point on the bottom of the plug, so that you could test the integrity of the fuse without taking it out of the plug. 

Light on a hair dryer? I hadn't seen that. We have one of those portable burners though, that has two burners and plugs into 120V. And it does have a green light though to show it plugged in. Probably a safety to remember to unplug when not in use.

I have an electric fireplace that has a lighted power symbol that lights red when the unit is plugged in but turned off and turns green when it's on . The dumb thing is when it's on , both the indicator and the display turn off after a few seconds so if you had turned off the fire effect and just had on the heat setting when the heat cycles off the whole thing is dark, Iv'e forgot about it and left it on all day before. i don't have a problem with the display timing off but the power indicator should stay on regardless !

Today i helped somebody fix an IR radating space heater with 4 identical heating elements, all facing in the same reflector in the same direction. The thing have 2 switches, first is OFF-I-II and second is a thermostat

In position "I" heating elements A and B are on all the time, regardless of thermostat on/off clicking. They are just permanently on

In position "II" all 4 heating elements are on, A and B will stay on all the time, C and D will switch on/off with the thermostat

My conclusion is that whoever wires them at the factory wires them out of the blue and without any logic. The same could be with the indicator...