NEVER insert a changing tool

[L4R3L2]

"NEVER insert a changing tool into the lock unless the lock's cover is in place."

So goes the typical warning. But, why? I understand that even a slight angle will affect the true dialing numbers, but is there something more damaging than that to consider?

I have practice locks with the back covers off. I mount them this way because I cut my spindle to length for four wheel locks so I can use one dial for all the locks. I've been changing the combinations without the covers in place, taking care that it is fully inserted at the right position with the tip in the pivot hole, and I hold it as straight as I can. So far, no problems, but I thought I'd pose this here in case I'm missing something.

[MartinHewitt]

The second possible issue is, that the change tool can partly slip out if you are not careful. When you turn the tool while it is not fully inserted you get some wheels tight and some wheels loose. Then someone locks the door with a loose wheel. Not fun!

[SafecrackinSammmy]

The tabs on the back cover determine which direction and how far the change tool will turn. And that all of the wheel hubs turn equally so that they are fully locked or unlocked for changing. Its a precise mechanism.

If you need to reset a lock with an unknown combination, you can always use a straightened paper clip etc. to walk the wheels around to the change key dimple in the case, then replace the cover and use the the change key.