LOL - The manual states you should calibrate if you move away from your usual flying area. My rule of thumb is to calibrate if I travel 150 miles from where I last calibrated. Probably being over cautious and 300 miles would be a satisfactory rule of thumb.
Ones location; proximity to magnetic forces or physical objects (iron) that would deflect a compass x degrees has to be considered to get an accurate calibration. There are those who calibrate every flight to err on the side of caution. I recall one bloke who calibrated on the top of a parking garage only to have his drone fly wacky - didn't consider the hidden concrete reinforcing rebar. Oops.
What is being calibrated is the magnetometer - the compass that guides the drone as it flies. The earth’s magnetic field changes depending on where you are, if you move your drone a large distance (several hundred miles) the drone will likely misread its heading and fly a few degrees off ones intended line.
Are there good places and bad places to calibrate your drone? Likely answer is "yes". If you want to calibrate before every flight, go for it. If you don't, fine. Just be smart about it one way or the other.
Oh yeah, don't store your drone in a box of magnets, or next to your car's massive sub woofer - I never do.
"Hey grandpa, why do you wear your hat sideways?"
"It keeps Martians away."
"Grandpa, that's just crazy."
"You don't see any Martians, do you?!"