I always calibrate my compass but today almost found out first hand what could happen. Taking off from the same spot as last time and didn't calibrate. Auto-takeoff and within seconds I sense something is wrong. My indicators have satellites I got the safe to fly go-ahead, but no good. Phantom is drifting in air and my weak manual skills had to be used to land her. Find a patch of grass close to a metal fence, land right beside the fence with the winds blowing me around, safely landed but my propellers sliced the fence and broke. She didn't even tip over just propeller damage. Replaced and calibrated. Next flight was as smooth as always.
Just a heads up, always calibrate your goods.
I have never had issues. Had a phantom 1 since they first came out only calibrated once.
My Phantom 2+ have had around 70 flights only calibrated once, no issues
And 40 flights on th p3 only calibrated once no issues.
You may have been near a metal surface or underground metal pipes could have caused an issue. Calibrating to much can be a bad idea also as its still possible to get a bad compass calibration. The more you do this, the greater the risk of a bad calibration.
All that will happen is it will toilet bowl and can control it and land easy, and taking off you will know in less than 1 minute it's not right.