Here we go again....
This has been discussed in numerous threads. It's not just 'some folks' that don't calibrate every time just because they happen to be stubborn.
The reason NOT to calibrate the compass is because a known GOOD calibration can NEVER cause a lot of trouble, even after you traveled 100 miles. The only thing you would notice is that it wouldn't fly perfectly straight lines anymore. Then it's time to calibrate.
The chance that you do a completely WRONG calibration, somewhere in the field, where you have no idea what interference might be present, is quite severe, and a cause for many fly aways (during RTH while flying beyond VLOS for instance, "it just never came back"......).
The toilet bowl effect is normally a IMU matter. Just as the magnetic compass, it is sensitive to magnetic fields. Did you have anything on you that might have caused interference? Or during transport? Subwoofer in the trunk?