it's a minor cost to add them. fractions of a second to do the comparison.
probably a millisecond at most
the cost fo not having 443 is that 443 wont be treated as https.
the reason that CA Support normally suggests 80 as well is that bouncing between content servers and cookie providers has a possibility of switching to http as a course of action, and having 80 there makes it flip back to https for sure.
in honesty, i think that most implementations can get away with 443 and not 80, but i would recommend 80 on the chance of an error occurring.
-Josh