As with all, you are going to have it based on many things.
How long has it been since last operation?
When was is used in a different location?
Are the camera and gimbal performing as they should?
I personally calibrate for every job and every location change.
In U.S. terms, think of this as your gun; you clean and inspect before and after every use. Heck, sometimes you just take it out to even look at it and wipe off a few finger prints and dust.....this is how you should look after your UAV, and then some.