I’m puzzled that so many are in such an all fired rush that they can’t spend about a minute to twirl their bird twice. The old adage if it ain’t broke fix hardly applies here, rather fly in haste and possibly repent at leisure to coin a phrase. Its hardly a chore.
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It’s nothing about being in a rush. It’s far more simple.
Seven years of early P2 and M1P … and just 1 calibration … when I first bought the P2 … and nothing has gone wrong once. Probably >5,000 flights all over Europe.
I can easily point you to reports of “this happened / that happened / disaster” after people had recalibrated their compass.
As mentioned by several people above, and particularly in the case of more recent models than my P2, they’ll tell you if it’s needed. Mine never have.
Statistically, in my experience, it’s totally just unnecessary for every flight. It’s that simple.
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The Earth’s magnetic field on the whole is constant. It does vary very slightly due to variances in land composition, but in the majority of cases this is negligible. Interesting fact though the Earths North Magnetic Pole is always shifting but the rate of change is that slow that the impact on a drone will take more time than DJI artificially limit the lifespan of their products to anyway.
The UK landmass longitudinally is not particularly large so there’d be little, if anything, to be gained from recalibrating at different locations as the change in offset would be very small. However on the CONUS this is not the case as there is a significant change in offset between New York and Los Angeles.
If you are constantly being asked to recalibrate your compass you should start by looking at the environment you intend to take off from. I carry a traditional Silva liquid compass in my bag as a backup on the off chance I get the prompt to recalibrate. This way I can divine and locate the source of the interference. Every build I have completed is calibrated once in an area that I know is free of any magnetic anomaly. Therefore if I’m in another area whereby I get prompted to recalibrate I know that I need to move. For if I were to recalibrate and then ascend out of the influence my compass would no longer be calibrated for the Earth’s true magnetic field which could, at best, lead to an erratic flight.
Confession Time 
. On a build using an APM flight controller I had inadvertently set the compass profile 180degrees offset from its actual orientation. Surprisingly nothing bad happened. I just kept hearing voice announcements from the ground station that the direction of travel did not correspond with the assumed heading.
Regards
Nidge.
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More than where the pole is, the magnetic declination (angle it deviates from true north) at any location is perhaps more significant.
A change in location can have a greater significance … but across Europe there’s little change.
Flying a couple of thousand miles south of Tasmania might be entertaining? 
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Firmware has a declination table as far as I’m aware.
Calibrations purpose is to measure the magnetic field of the aircraft so it can be removed from the equation.
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Interesting discussion - I fly a lot in SE Asia and have only recently come to the UK - because when home I’m “nearer” china and have noticed an increase in the number of available satellites ( which surprised me ). When home I find i am not asked by the drone to calibrate compass, but since I have been here in Wales I am asked much more often. All very odd really but I’m sure theres a scientific answer which might be interesting. Im beginning to wonder if the “spy” satellites up there suddenly pop up in the drones count ? Mind you, they aint “spy” then are they 
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Them un-named Chinese ones aint too bad either over SE Asia - funny how there are always 20+ lol
Turn the drone on and that little icon that “searches” for satellites is blurry cos so many appear in milliseconds lol
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