According to the manual, calibration is only necessary if the app prompt you to do so.  Several videos indicate you must calibrate when flying in a different location.  Which is it?

Myself and many others only calibrate Compass when prompted.  I've probably only done this a total of 10x with ALL of my DJI products.  FYI, I've NEVER done an IMU calibration on any DJI product.

Personally, the only time I calibrate anything is the Compass and only if I have moved a significant distance (200miles+) or I get unexpected ATTI switch, usually an indication of compass requiring a calibration. So far I have not calibrated the Spark and flown it straight out of the box and it has been fine.

Lots of pilots have been grounded carrying out un-necessary calibrations that then fail, IMU, Vision and Gimbal, never done those on my Mavic and never had a problem.