Well, speaking of stock MG kits, even if you are not intent to kitbash, the assembled model typically looks unfinished. When you start getting into resin mods, those are usually just a solid color (mine have been off-white or light blue) so color-matching is necessary to have the model look complete.
That's just my experience, which isn't all that extensive. I still don't have an airbrush.
That's just my experience, which isn't all that extensive. I still don't have an airbrush.