With US ZIP (postal) codes, padding with zeroes can actually be ambiguous because we have "zip+4" which is often stored as two fields, but just as often concatenated into a single representation. If you have a zip+4 of "05555-0444" in two fields that each lose leading zeroes, and then concatenate to "5555444" you can't reconstruct it with certainty (00555-5444 or 05555-0444 or 55554-0044).

I had a package get seriously delayed one time because it kept being sent to a city whose 5 digit zip code was equal to [my 5 digit zip code, less its leading 0, and the first digit of my +4]. Fun times.