I’m going to start out with that this really does not matter in most use cases, but if you need the compass for something, you might want to pop off any magnetic phone case you have and keep your wristwatch/smart tracker away from the phone.
While there are some crazy use cases I could quote, the realistic impact is if you’re walking somewhere and using Google Maps the directional indicator can be off a bit. I’ve been driving before and the directional wasn’t the same as the street I was on (I was still in walking mode we just hopped in the car as it was several blocks further than I expected.)
I guess it could be completely off but what magnetic cases seem to do on my S21 and my Pixel 7 Pro are just make the directional indicator be about 10% off.
I will note that once you take the magnetic case off you’re right back to normal. It’s not like it ruins anything and I break out the compass so infrequently it’s not an issue.
Also on the wristwatch front – I use a Withings Scanwatch on a regular basis, if it gets within two inches of the phone the compass tends to go wonky.
Your watch/case/phone experience may differ, and as I prefaced with – this is not an issue in most cases.
But if you happen to find yourself looking at Google Maps while you’re wandering around a theme park and unsure what direction you’re actually looking… move that hand with the watch on it and see if things make a little more sense.
Google Maps, as a note, does not need this to get you from point A to B as it uses GPS and as far as it’s concerned you’re going in the right direction while looking backwards in some cases.