Depending on the means used to calculate the distance, it could start throwing errors if the coordinates are far enough away from the WCS origin (we get this quite often with models in mm). For example, if the numbers need to be squared in the distance calculation. Progressive checking (e.g. first X, then Y, then Z) may be of some benefit, since if the first value is too far off the rest of the values are irrelevant, same with the second. Changes it from multiple square/root operations to a comparison of reals.
There may also be some other concerns - doesn't (distance...) use some current dimension style variables for precision?