Not to mention tripping on roots, twisting your ankle in that little divot in the trail, missing the trail and going head-long into an alder thicket/thorns/boggy area (pick one or all of the above) or of course going right pass the cache that is right in plain view.
For the record, I agree with you . . . this thread kind of reminds me of the cell phone warnings on the gas pumps. While the older cell phones may have had some potential to cause a spark, research on the newer tech seems to indicate that the potential hazard is over-stated, but nevertheless we have the warning labels . . .