Why do DPs and ACs like removing lenses so much?

[Mei Lewis]

Most of the ones I’ve worked with like to remove the current lens before packing the camera away. Is there some reason for that beyond force of habit and superstition?

I like removing and changing lenses as little as possible, to reduce the chance of junk getting inside the camera, particularly on the sensor.

 

[David Mullen ASC]

It's safer for transporting if the camera and lens are packed separately, the mount is a weak point, especially for heavier zoom lenses.

[Brian Drysdale]

With 35mm sized cameras the cases usually don't allow you to pack the cameras away in a ready to shoot state. The reasons being as David says and the rental companies are probably protecting their investment, also the cases would become rather large. 16mm and 2/3" cameras traditionally do get packed in a ready to shoot state when used on documentaries etc because you may miss the shot, but the lenses are much lighter. However, you should remove the lens if you're freighting the camera or flying with the gear.

[David Mullen ASC]

The mount is not only a weak point, but if the lens is flexed too much at the mount, your back-focus may be thrown off.