The first processor on my master bus is a tube or solid-state saturation plugin. The real-world example of this effect would be the master bus of an analog console. It is actually one of the main reasons why analog consoles are still used; they have a nice character, while a normal DAW master bus doesn't have any character of its own. Most consoles use solid-state technology, but the plugins which model this effect are very rare. That's why most people have to settle for tube saturation. It's a shame but tube saturation is not a bad alternative at all!