riding on a flat tyre

ok got to my bike the other night after work and the tyre was flat. it was 4 psi when I got to the servo.
It's only a slow leak from a bit of metal. not a nail, hard to tell what it is exactly, it's still in there.
planning on getting it plugged cos there's still a couple of thousand k's on the tyre.
but...
having ridden it while pretty much flat I recall reading that this will damage the tyre. so what's the story?
what is actually damaged and what are the possible consequences ?
would you commute on it for another month?
going to go to race replica to get it done ... thought I'd check them out since Kris has been posting here.
It's only a slow leak from a bit of metal. not a nail, hard to tell what it is exactly, it's still in there.
planning on getting it plugged cos there's still a couple of thousand k's on the tyre.
but...
having ridden it while pretty much flat I recall reading that this will damage the tyre. so what's the story?
what is actually damaged and what are the possible consequences ?
would you commute on it for another month?
going to go to race replica to get it done ... thought I'd check them out since Kris has been posting here.