I was thinking yesterday about mouldlines and if there was a fluff justification for ever leaving them on your models. I thought up a few and I will put them here to see what people think and what else you all can come up with.
Death Guard/Nurgle in general: Joke - it's called mouldline 'cleaning' - self explanatory.
Astra Militarum: The imperium does not care enough for the common soldier to remove mouldlines from their armour.
What do you think? Any others you can come up with?