Hello everyone, I have a quick question for you. How frequently should you perform compass and IMU calibration? The reason I’m asking is that I flew my Air 3s yesterday and noticed it wasn’t flying in a straight path. Since it had never been calibrated before, I decided to land it and carry out the compass and IMU calibration, which resolved the issue.
Only when you have an issue like you had, after a crash or if the software prompts you
Cheers 
One other thing you may need to check is where did you take off from - was it close to metal or from metal like your car as that will also mess up the compass a bit too. As Sparky has said - I have only ever done it when I do a firmware update or prompted to do so.
Ditto … other than, as yet, and in over 12 years and five different drones, I’ve yet to recalibrate either .. and that despite flying in UK, France, Italy, Germany, Belgium, Holland, Switzerland and Austria and many firmware updates in all that time and moving my take-off location has always cleared any initial magnetic interference warnings. 
Only in back garden
All sorted new