Missing insulation at chill water and dual temperature pipe usually prompts its own repair after dripping condensation becomes a problem, but not always.  Given the inherent difficulty in insulating smaller diameter pipe, as well as pumps, strainers, and other odd shaped piping components, insulation is far more likely to be either missing or inadequate.  Strapped or tied together insulation jackets, while providing some aesthetic benefit, offer no protection whatsoever to any cold pipe surface.

As for all other forms of corrosion, the impact of missing insulation is greatest at any smaller diameter threaded steel pipe having inherently lesser wall thickness.  In addition, missing insulation at a 1 in. top vent or bottom drain then provide access for moisture to enter, migrate, and condense to produce damage to the larger diameter mains as well.  The damage potential is very much increased in very humid parts of the country such as Houston and Miami, and a far lesser threat in Phoenix or Anchorage.