It depends on the situation. In a total-stranger situation there are simple, pre-written modules the host can use and, if time is truly short, there are all sorts of resources to create pre-generated characters as well. That means prep-time is relatively low and people new to the hobby/system don't have to get bogged down by the numbers right away. Obviously, writing a game and making characters from scratch generally leads to more interesting campaigns, but that's not always on the table. Check out DCC RPG if you're interested in easy to run modules with tons of tools for quickly generating characters.